Systems, Program Product, and Methods For Synthesizing Heat Exchanger Networks That Exhibit Life-Cycle Switchability and Flexibility Under All Possible Combinations of Process Variations

ABSTRACT

A system, methods, and user-friendly program product to optimize energy recovery for a process or cluster of processes under all possible combinations of given process changes and stream-specific minimum temperature approach values without enumeration, are provided. The systems, methods, and program product can include steps/operations to synthesize multiple heat exchanger network designs according to different process variations schemes, analyze the impact of process variations on each heat exchanger network, and identify which design provides a more optimal heat exchanger network design and which process variation scheme represents a more optimal flexibility index.

RELATED APPLICATIONS

This patent application is a non-provisional patent application of U.S.Provisional Patent Application No. 61/356,900, filed Jun. 21, 2010,titled “Systematic Synthesis Method and Program Product For HeatExchanger Network Life-Cycle Switchability and Flexibility Under AllPossible Combinations of Process Variations” and U.S. ProvisionalApplication No. 61/256,754, filed Oct. 30, 2009, titled “System, Method,and Program Product for Synthesizing Non-Constrained and ConstrainedHeat Exchanger Networks and Identifying Optimal Topoloy for FutureRetrofit,” and is a continuation-in-part of U.S. patent application Ser.No. 12/715,255, filed Mar. 1, 2010, titled “System, Method, and ProgramProduct for Targeting and. Optimal Driving Force Distribution in EnergyRecovery Systems” which is a continuation of U.S. patent applicationSer. No. 11/768,084, filed on Jun. 25, 2007, now U.S. Pat. No.7,698,022, titled “System, Method, and Program Product for Targeting andOptimal Driving Force Distribution in Energy Recovery Systems,” whichclaims priority to and the benefit of U.S. Provisional PatentApplication No. 60/816,234, filed Jun. 23, 2006, titled “Method andProgram Product for Targeting and Optimal Driving Force Distribution inEnergy Recovery Systems,” U.S. patent application Ser. No. 12/767,217,filed Apr. 26, 2010, titled “System, Method, and Program Product forSynthesizing Non-Constrained and Constrained Heat Exchanger Networks,”U.S. patent application Ser. No. 12/767,275, filed Apr. 26, 2010, titled“System, Method, and Program Product for SynthesizingNon-Thermodynamically Constrained Heat Exchanger Networks,” U.S. patentapplication Ser. No. 12/767,315, filed Apr. 26, 2010, titled “System,Method, and Program Product for Synthesizing Heat Exchanger Networks andIdentifying Optimal Topology for Future Retrofit,” and U.S. patentapplication Ser. No. 12/575,743, filed Oct. 8, 2009, titled “System,Method, and Program Product for Targeting and Identification of OptimalProcess Variables in Constrained Energy Recovery Systems,” eachincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This present invention relates to the field of energy recovery systems,program product, and related methods.

2. Description of the Related Art

Many different types of processes consume multiple steam levels andelectricity to obtain an output result, or to produce a required productor compound. For large-scale processes that, for example, consumesignificant amounts of fuel and steam, it is preferable to optimize theconsumption of energy through careful operation, design orreconfiguration of the plant and the equipment used. Further, in someindustrial manufacturing processes, specific streams of material flowsneed to be supplied to different types of equipment and machinery atspecific temperatures. These material flows may need to be heated orcooled from an original starting or supply temperature to a targettemperature. This, in turn, requires the consumption of steam to heatspecific streams and consumption of water, for example, to cool downspecific streams.

The total energy employed or consumed by the industrial manufacturingprocesses can be optimized to a global minimal level, for example,through careful placement and configuration of specific material streamswith respect to one another. There may be, for example, the potentialfor hot streams that require cooling to be placed in proximity with coldstreams that require heating. Streams having thermal energy alreadypresent that need to be removed (waste heat) or streams that need tohave heat added can be associated with one another to optimize theenergy consumption of the process. A network of heat exchangers can besynthesized to provide a medium for utilizing this waste heat to provideheat to those streams that need to have heat added. This heat exchangernetwork can be a very important sub-system in any new plant.

As such, the heat exchanger network synthesis problem has arguably beenone of the most studied problems in the field of process synthesis inthe last four decades. The systematic synthesis of heat exchangersnetwork, however, has proven to be a challenging task. During the lastthree decades a considerable number of methods have been proposed andutilized in commercial software and/or academia. These methods arereferenced in the two famous review papers of T. Gundersen and L. Naess,“The Synthesis of Cost Optimal Heat Exchanger Networks,” Computers andChemical Engineering, vol. 12, pp. 503-530 (1988), and of Kevin C.Furman and Nikolaos V. Sahinidis, “A Critical Review and AnnotatedBibliography for Heat Exchanger Network Synthesis in the 20^(th)Century,” Industrial Engineering & Chemistry Research vol. 41, pp.2335-2370 (2002).

The state-of-the-art software widely used in industry for initialsynthesis of the heat exchange network (HEN) includes, for example, anAspenTech Inc. product known as Aspen Pinch, a Hyprotech Inc. productknown as HX-NET (acquired by AspenTech), a KBC product known as PinchExpress, and a UMIST product known as Sprint, which attempt to addressthe heat exchanger network synthesis problem using the well known pinchdesign method, followed by an optimization capability that optimizes theinitial design created by the pinch design method through use of streamssplit flows in streams branches and manipulates heat exchanger duty byutilizing the global network heat recovery minimum approach temperatureas an optimization variable, in a non-linear program to recover morewaste heat, shift loads among heat exchangers to remove small units,redistribute the load (duty) among units, and optimize surface area, ofcourse, always within the constraints of the topology determined usingthe pinch design method. The pinch design method, followed by theoptimization capability method, or combination of methods, has seen widespread acceptance in the industrial community due to its non-black boxapproach. That is, the process engineer is in the feedback loop of thedesign of the heat exchangers network such that the process engineer canmake design decisions that can change with the progress of the design.Recognized by the inventors, however, is that in all applications ofnear pinch and multiple pinches problems to the above softwareapplications, their respective calculations render a larger than optimalnumber of heat, exchange units. Also recognized is that, in addition,software applications that use the pinch design method or that use thepinch design method as a basis for its initial design followed by theoptimization option for branches and duties can not handle certainsituations/constraints/opportunities that can render better economics,for example, from energy, capital, or both points of view, which meansthat some superior network designs will never be synthesized using suchapplications.

Other methodologies include mathematical programming-based methods.Although such methods have been in academia since the late eighties,they are still not widely used on a large scale in industrialapplications for several reasons. For example, the computationalrequirements of such methods are substantial, especially for largeproblems, and the resultant solution, in general, can not guaranteeglobality. Additionally, besides the inherent disadvantage of the blackbox nature of such methods, the mathematical programming-based methodsrequire assumptions regarding problem economics, the types of heatexchangers used in the network (shell & tube, twisted tube, plate andframe types, etc.), the need to know the several utilities types andtemperatures beforehand, and the non-inclusive nature of the“transshipment model” used for streams matching and superstructureapplication, which explains why the pinch design method is still theleading method in industry, even with its inadequacies.

It has been recognized that heat exchanger network synthesis of bothswitchable and flexible heat exchanger networks under variations inprocess conditions, however, is more difficult than the nominal design.Nevertheless, although literature has been in existence since the lateeighties which has identified a desire for flexibility in the heatexchanger network design, apart from the stochastic methods (trial anderror approach) which also require unrealistic assumptions and which arevery difficult to implement by regular process engineers, there stillonly remains the pinch-based approach and the mathematicalprogramming-based methods.

As introduced above, the pinch-based approach remains the industrypractice even though it is in-systematic and needs iteration withoutguarantee to reach, at the end, a feasible and cost effective design. Inbrief, the pinch-based approach uses the pinch design method as a basisto develop a heat exchanger network that can handle process variations.It sets up multiple operating cases in a step which is in-systematic andad hoc. It then uses the pinch method to design individual networks foreach case. It then tries to merge the individual designs to form a finalone. Thereafter, it uses the disturbance and uncertainty scheme to testfor feasibility of the network in the face of the disturbances anduncertainty. If the network is not feasible, it again in-systematicallyadds contingencies to try to make it feasible. If still not feasible,the approach sets new multiple operating cases and repeats theprocedures iteratively. If the new loop renders a feasible network,optimize the network and recheck for feasibility. Again, ifinfeasibility arises, the problem is not solved and iterationin-systematically provides the only solution. Nevertheless, as notedabove, even with the requirement for a substantial amount of ad hocdecisions and iteration, the pinch-based approach is still leading inmost commercial software.

On the other hand, heat exchanger network synthesis, under varyingconditions for switchability and flexibility using mathematicalprogramming is even more difficult to use and inherently has myopicassumptions. For example, the mathematical programming approach can beextremely difficult because the nominal design one-period problem itselfis difficult to employ to try to solve industrial scale problems withoutextensively applying simplifying assumptions in the type of heatexchangers used, places of the service units, number of streams matchingmore than once, etc. As such, it is expected that applying such approachto a multi-period synthesis problem would be extremely difficult. It maybe particularly difficult to implement, for example, because fromindustry point of view, the basic assumption regarding the disturbancesand uncertainty schemes that define exactly each operating period at thedesign phase, is completely unrealistic.

Accordingly, recognized by the inventors is the need for an improvedsystem, program product, method or technique that can address any or allof the above optimization issues, particularly during the design stage,and which can minimize energy and capital costs for waste heat recoverythrough application of a systematic process prior to the actual design,construction or modification of actual plant and equipment.Particularly, recognized is the need for a systematic heat exchangernetwork synthesis method with life-cycle switchability and flexibilityunder all possible anticipated combinations process variations thatexhibits much better capabilities than the ad hoc in-systematic pinchapproach and that can render in all cases, a network design including anumber of the exchanger units that is less than or an equal to thenumber of heat exchanger units for the networks synthesized using thepinch design method, even when combined with heat exchanger duty andbranch optimization options currently implemented in commercialsoftware, for all types of problems to include pinched problems,problems with near pinch applications, as well as multiple pinchesproblems, that need both heating and cooling utilities, and problemsthat need only cooling or only heating utility (called thresholdproblems).

Also, recognized by the inventors is the need for improved methods,systems, and techniques that can address cases where the optimalsolutions can be provided by matching a hot stream with a hot stream ora cold stream with a cold streams, or partially converting a hot streamto a cold stream or a cold stream to a hot stream. Further, recognizedby the inventors is the need for improved methods, systems, andtechniques which can provide a guarantee of feasibility under a givenrealistic disturbance scheme, which can produce heat exchangers networkswithin the optimal number of units, which addresses life cycleswitchability and flexibility, and which can be used to calculateoptimal target temperatures for streams within a realistic operatingwindow range at the design phase under all possible combinations ofanticipated disturbances and uncertainty.

It is further recognized by the inventors that it would be beneficial ifthe heat exchanger network design, according to such methods, systems,and program product, were also such that the network was configured tobe “easily-retrofitable” in future times to allow for growth and/or forcontingencies such as, for example, those due to dramatic changes inenergy prices resulting in a need to operate under future time-dependentoperating modes, disturbances and uncertainty schemes. Notably, it isnot believed that the pinch design method could adopt retrofitabilityduring the design stage as it does not have a systematic method toselect an optimal set of supply temperatures, target temperatures,and/or stream specific minimum temperature, either in general, or basedupon a trade-off between capital and energy costs, in particular, andbecause its pinch design philosophy starts the design of the networkonly after selecting an optimal initial conditions including supplytemperatures, target temperatures, and network global minimum approachtemperature using, for example, the “SUPERTARGET” method which targetsfor both energy consumption and the heat exchanger network area at thesame time. Even by repeating such sequential philosophy using differentranges of supply and/or target temperature values, the resulting newnetwork structure would not be expected to consistently resemble theprevious network structure, in class, and thus, would result in arequirement for an undue expenditure in network reconciliation efforts,to try to form a continuum of common-structure heat exchanger networkdesigns which can be used to facilitate user selection of a physicalheat exchanger network structure satisfying both current user-selectedeconomic criteria and anticipated potential future retrofit requirementsand corresponding physical heat exchanger network development andfacility surface area of allotment based upon such selected design.

SUMMARY OF THE INVENTION

In grassroots heat exchangers network (HEN) design under frequentprocess variations in the form of disturbances and uncertainty, it isneeded to have a design that is not only cost effective but alsoswitchable and flexible along its life cycle to respond to differentoperating modes and/or face disturbances and uncertainty withoutaffecting process economics systematically and without iteration. Inaddition, it can be important for such design to be inherentlyretrofitable (easy-to-refit in the future) due to the ongoing changes inthe trade-off between capital cost and energy cost of energy systemsand/or process variation schemes. As such, and in view of the foregoing,various embodiments of the present invention advantageously providemethods, systems and program product for synthesizing a grass-roots heatexchanger network which addresses the difficult problems of designingheat exchanger networks under varying conditions with a simple yetsufficiently rigorous approach. Various embodiments of the presentinvention advantageously provide methods, systems and program productfor synthesizing a heat exchanger network under process variations withlife cycle switchability and flexibility and easy-to-implement futureretrofit, which can handle industrial-size problems, which can keep thedesigner in control for the synthesis of the network without forcinghim/her to use assumptions that confine the synthesized network tospecific inferior structures due to the use of inconclusivesuperstructure, which can allow the designer to test his/her novelsolutions for network synthesis that suffer constrained situationsaffecting energy consumption to include those normally faced inindustrial applications, and which can render a lesser number of unitsfor the same energy targets compared with pinch design approach for theproblems that exhibit multiple pinches and pinch with near pinchapplications.

Various embodiments of the present invention advantageously providemethods, systems and program product for synthesizing a heat exchangernetwork which can allow the designer to test his/her novel solutions fornetwork synthesis using realistic disturbance and uncertainty scheme,which can calculate a best estimate for operating cost calculation todevelop networks that exhibit a minimum number of units with a minimumvalue for the maximum-required surface area, and which can performsystematically and without iteration, in contrast to the conventionalpinch-based approach. Various embodiments of the present inventionadvantageously provide methods, systems and program product forsynthesizing systematically a heat exchanger network having life-cycleswitchability and flexibility as well as easiness in heat exchangernetwork future systematic retrofitability, that can perform calculationsat the design phase under all possible combinations of disturbances anduncertainty of optimal target temperatures for streams havingoperational conditions with an operating window range, and that canestablish a high fidelity relationship between energy cost versuscapital cost verses process-inpact-cost due to a lack of flexibilityresulting from deviations in designed anticipated disturbances anduncertainty and/or new operating modes, systematically and withoutenumeration.

Particularly, various embodiments of the present invention provide asystem to synthesize a grass-roots heat exchanger network for a processor cluster of processes having a plurality of hot process streams to becooled and a plurality of cold process streams to be heated and toidentify optimal heat exchanger network topology. According to anembodiment of the present invention, such a system can include a heatexchanger network synthesizing computer having a processor and memorycoupled to the processor to store software and database records therein,and a database stored in the memory (volatile or nonvolatile, internalor external) of or otherwise accessible to the heat exchanger networksynthesizing computer. The database can include a plurality of datapoints, e.g., in the form of data pairs, indicating potential ranges ofvalues for process stream operational attributes (e.g., (Ts), (ts),(Tt), (tt), (FCp)) for each of a plurality of process streams, a set{ΔT_(min) ^(i) [L:U]} of lower and upper stream-specific minimumtemperature approach boundary values ΔT_(min) ^(i) between streams,streams initial types, streams matching constraints, one or moreinterval global utility consumption value [Qh], [Qc], and/or indicia ofthe lower and upper bound of the pinch region boundary. Note, althoughrange/interval values are preferred, the various values including atleast some of the operational attributes, stream-specific minimumtemperature approach boundary values between streams, and the globalutility consumption value, can be in discreet form.

The system can also include heat exchanger network synthesizing programproduct stored in memory of the heat exchanger network synthesizingcomputer and/or as a stand-alone deliverable. According to a preferredconfiguration, the program product provides systematic synthesis of heatexchanger networks for switchability and flexibility under all possiblecombinations of process variations in grassroots applications witheasy-to-implement life-cycle retrofitability for a process or cluster ofprocesses using a plurality of resource streams, and can analyzecapital, economic, process-impact-costs in order to design an optimalheat exchanger network based on an analysis of the effect of differentsupply conditions feasibility on target temperatures as well as theeffect of target temperatures flexibility, on the process as a whole.

Notably, the inventors have recognized that the capital and economiccosts of maintaining target temperature values for certain processstreams within a certain range of values may outweigh the cost ofaccepting a deviation in such target temperature values. That is, thecapital and operational costs necessary to provide supply conditionshaving 100% feasibility may vastly exceed the process-cost impact of acertain deviation in target temperature. This may also hold true for thecost of achieving 99%, 98% . . . X % feasibility. Accordingly, theprogram product can advantageously include instructions that whenexecuted by a computer such as, for example, the heat exchanger networksynthesizing computer, cause the computer to analyze a triple trade-offamong energy cost, heat exchanger network capital cost, and economicimpact on the process in order to identify an optimal heat exchangernetwork process variations scheme, for example, representing an optimalflexibility index.

Specifically, the program product, according to an embodiment of thepresent invention, can include instructions that when executed by acomputer such as, for example, the heat exchanger network synthesizingcomputer, cause the computer to perform various operations including theoperation of receiving various input data including a plurality of datapoints indicating potential ranges of values for operational attributesfor each of a plurality of process streams, a set of lower and upperstream-specific minimum temperature approach boundary values betweenstreams, streams initial types, streams matching constraints, one ormore interval global utility consumption values, and/or indicia of thelower and upper bound of the pinch region boundary.

The received operational attributes can include a plurality of sets ofprocess stream supply attribute values associated with a plurality ofheat exchanger network process variations schemes. In a typicalconfiguration, for example, each heat exchanger network processvariations scheme incorporates a plurality of sets of process streamsupply attribute values to include, for example, a set of supplytemperatures (Ts, ts), a set of target temperatures (Tt, tt), and a setof a plurality of heat capacity flow rates (FCp) each separatelyassigned or otherwise associated with a corresponding one of the hotand/or cold process streams. Each set of supply temperatures (Ts, ts)can include a set of a plurality of hot process stream supplytemperatures (Ts) assigned or otherwise associated with a correspondingplurality of hot process streams and can include a set of a plurality ofcold process stream supply temperatures (ts) assigned or otherwiseassociated with a corresponding plurality of cold process streams.Similarly, each set of heat capacity flow rates (FCp) includes aplurality of heat capacity flow rates (FCp) assigned or otherwiseassociated with a corresponding plurality of the process streams (bothhot and cold). Such data can be directly imported by an experiencedtechnician and/or otherwise identified through estimation, historyanalysis, or expert guidance based upon material and fluid productproperties.

Each set of process stream supply temperature attribute values of eachseparate heat exchanger network process variations scheme can have alevel of supply temperature feasibility being different from the levelof supply temperature feasibility for each other of the plurality ofheat exchanger network process variations schemes, and/or each set ofheat capacity flow rates of each separate heat exchanger network processvariations scheme can have a level of heat capacity flow ratefeasibility being different from the level of heat capacity flow ratefeasibility for each other of the plurality of heat exchanger networkprocess variations schemes.

According to an embodiment of the present invention, the operations alsoinclude synthesizing a plurality of heat exchanger network designsaccording to a corresponding different one of a plurality of heatexchanger network process variations schemes. The operations can alsoinclude determining capital and operating costs associated withemploying a first heat exchanger network process variations scheme(e.g., having 90% flexibility) on a first of the heat exchanger networkdesigns, and determining capital and operating costs associated withemploying the second heat exchanger network process variations scheme(e.g., having 100% flexibility) on a second of the heat exchangernetwork designs.

The operations can also include applying a supply attribute range ofvariation of the one of the process streams according to the second heatexchanger network process variations scheme (e.g., having 100%flexibility) defining a second supply attribute value range of variationto the supply attribute for the one of the process streams for the firstheat exchanger network design (e.g., having 90% flexibility) defining afirst supply attribute value range of variation and observing orotherwise identifying an associated change in target temperatureresulting from application of the second supply attribute value range ofvariation thereto to thereby identify a cost impact employing the 100%variations scheme on a heat exchanger network designed for 90%variations scheme.

Accordingly, the operations can also include determining aprocess-cost-impact of a deviation in target temperature range ofvariation for one or more of the process streams for the first heatexchanger network design responsive to application of the second supplyattribute value range of variation to the supply attribute (e.g., supplytemperature and/or heat capacity flow rate) of the one of the processstreams for the first heat exchanger network design, analyzing a tripletrade-off between estimated energy operating cost of the respective heatexchanger network design, estimated heat exchanger network capitalcosts, and estimated process-cost-impact. The operations can alsoinclude determining the first heat exchanger network design according tothe first heat exchanger process variations scheme to be the optimalheat exchanger network design and the first heat exchanger networkprocess variations scheme to represent the optimal system levelflexibility index when the difference in capital cost and operating costbetween the first and the second heat exchanger network designs ishigher than the process-cost-impact.

The operations can also or alternatively include determining a targettemperature range value for the one of the process streams of theplurality of process streams defining an expected sub-optimal targettemperature range value responsive to the operation of applying thesecond supply attribute value range of variation to the supply attributeof the one of the process streams for the first heat exchanger networkdesign, and determining a target temperature range value for each otherof the plurality of process streams responsive to the step of applyingthe second supply attribute value range of variation to the supplyattribute of the one of the process streams for the first heat exchangernetwork design.

The operations can further include determining the first heat exchangernetwork design according to the first heat exchanger process variationsscheme to be the optimal heat exchanger network design and the firstheat exchanger network process variations scheme to represent theoptimal system-level flexibility index when the difference in capitalcost and operating cost between the first and the second heat exchangernetwork designs is higher than the process-cost-impact. Note, in thisexemplary configuration, the process-cost-impact of a deviation intarget temperature range of variation for one or more of the processstreams for the first heat exchanger network design includes an impactof the expected sub-optimal target temperature range value for the oneof the process streams and any changes in the target temperature rangevalue for each other of the plurality of process streams on totalprocess economics resulting from application of the second supplyattribute value range of variation on the first heat exchanger networkdesign.

The operations can also or alternatively include analyzing, for each ofthe plurality of heat exchanger network designs associated with thecorresponding plurality of the heat exchanger network process variationsschemes, the triple trade-off between estimated energy operating cost ofthe respective heat exchanger network design, estimated heat exchangernetwork capital costs, and estimated process-cost-impact at each of aplurality of individual process stream flexibility levels, andperforming at least one of the following priority levelassignment/development operations: determining stream-specific targettemperature flexibility level priority by economic impact on the processas a whole defining a stream-specific-flexibility-level prioritizationscheme between each of the plurality of process streams responsive toapplication of a plurality of different supply or temperature ranges ofvariation to each of a plurality of process streams under evaluation;assigning a stream-specific target temperature flexibility prioritylevel to each target temperature range of variation of each of theplurality of process streams having a substantial economic impact on theprocess as a whole; determining for the plurality of process streams astream-specific flexibility priority list including a separatestream-specific flexibility level associated with each separate one ofthe plurality of process streams, whereby at least two of thestream-specific flexibility levels being different from each other, anddetermining for the plurality of process streams a stream-specifictarget temperature flexibility priority list including a plurality ofdifferent stream-specific target temperature flexibility levels for eachseparate one of one or more of the plurality of process streams.

The operations can also or alternatively include determining for theplurality of process streams a supply attribute criticality list ofprocess stream supply temperature ranges of variations including aseparate range of variations for each of the plurality of processstreams wherein a deviation in the range of variation thereto results ina substantial economic impact on the process as a whole, and/ordetermining for each of the plurality of process streams a supplyattribute criticality list of heat capacity flow rates range ofvariations wherein a deviation in the heat capacity flow rate range ofvariation thereto results in a substantial economic impact on theprocess as a whole.

Various embodiments of the present invention also advantageously providemethods to synthesize a grass-roots heat exchanger network for a processor cluster of processes having a plurality of hot process streams to becooled and a plurality of cold process streams to be heated and toidentify optimal heat exchanger network topology. The methods caninclude, among others, various steps substantially coinciding with thosedescribed with respect to the program product along with the processsteps for physically constructing a current heat exchanger network,allotting appropriate real estate/surface area for future retrofit,identifying retrofit requirements, and retrofitting the current heatexchanger network to match one of the network designs provided in thecontinuum of designs having a common process-to-process structure.

Various embodiments of the present invention provide a user-friendlymethodology for advanced systematic synthesis of a heat exchangernetwork under variations, which can benefit heat exchangers networksynthesis and waste heat recovery applications of new plant designs andits future retrofit in a world of fast dynamic with significant changesin energy availability and prices. Various embodiments of the presentinvention provide several folds of commercial benefits. First, variousembodiments of the present invention provide unique advancedmethodologies that can be easily automated in existing software orprovided as separate user-friendly software to optimally design energyrecovery systems in industrial facilities. Industrial companiesutilizing such methodologies can be expected to have an edge from energyefficiency consumption and pollution minimization points of view indesigning and operating their facilities. An estimated 5% improvement inenergy efficiency optimization beyond what could be currently obtainedfrom the state-of-art tools and technology, due to the application ofone or more embodiments of the present invention, can result in savingof tens of millions of dollars per year to implementing company inenergy consumption and huge saving in projects capital too. Second, thecommercial development of the various techniques/methods and algorithmsdescribed herein can, by themselves, provide independent tools foroptimizing facilities from waste energy recovery system synthesis andfuture retrofits point of view. Finally, along with various othercommercial benefits, the various methods/techniques can employ to formpart of a “centre of excellence” or “hot-house” in an energy efficiencyoptimization business.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features and advantages of theinvention, as well as others which will become apparent, may beunderstood in more detail, a more particular description of theinvention briefly summarized above may be had by reference to theembodiments thereof which are illustrated in the appended drawings,which form a part of this specification. It is to be noted, however,that the drawings illustrate only various embodiments of the inventionand are therefore not to be considered limiting of the invention's scopeas it may include other effective embodiments as well.

FIG. 1 is a schematic block diagram of a system to synthesize agrass-roots heat exchanger network for a plurality of process streamsand to identify optimal heat exchanger network topology according to anembodiment of the present invention;

FIG. 2 is a diagram illustrating generation of temperature stepintervals included with a diagram of a heat exchanger network synthesisimplementation for a simple threshold problem for an industrial processaccording to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a physical structural configuration ofa heat exchanger network synthesis implementation for the industrialprocess shown in FIG. 2 according to an embodiment of the presentinvention;

FIG. 4 is a diagram illustrating generation of temperature stepintervals included with a diagram of a heat exchanger network synthesisimplementation for a simple pinched problem for an industrial processaccording to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a physical structural configuration ofa heat exchanger network synthesis implementation for the industrialprocess shown in FIG. 4 according to an embodiment of the presentinvention;

FIG. 6 is a block flow diagram illustrating calculation of individualheat exchanger network design details according to an embodiment of thepresent invention,

FIG. 7A is a schematic diagram of a single heat exchanger illustratinginput and output connections and nomenclature;

FIG. 7B is a graph illustrating a time-dependent temperaturedifferential between cold and hot stream temperature for the heatexchanger shown in FIG. 7A;

FIGS. 8-10 are schematic diagrams of a single heat exchanger graphicallyillustrating a process for determining a heat exchanger duty and surfacearea according to an embodiment of the present invention;

FIG. 11 is a tabular description of an input file for a program fordetermining heat exchanger duty surface area according to an embodimentof the present invention;

FIG. 12 is a tabular description of an output file produced by a programfor determining heat exchanger duty surface area according to anembodiment of the present invention;

FIG. 13 is a block flow diagram illustrating a process for determiningan optimal heat exchanger network design and flexibility index accordingto an embodiment of the present invention;

FIG. 14 is a block flow diagram illustrating a process for selecting astream-specific set of target temperature values rendering an optimalheat exchanger network design according to an embodiment of the presentinvention;

FIGS. 15-17 are schematic diagrams illustrating an application ofsuccessively lower minimum temperature approach values to the sameindustrial process to produce a series of heat exchanger networks eachhaving a common process-to-process heat exchanger network structureaccording to an embodiment of the present invention;

FIGS. 18-20 are schematic diagrams illustrating an application ofsuccessively lower supply temperature interval values to the sameprocess streams of the same industrial process to produce a series ofheat exchanger networks each having a common process-to-process heatexchanger network structure according to an embodiment of the presentinvention;

FIG. 21 is a schematic block, diagram of a method of determining heatexchanger design details for each heat exchanger of a network accordingto an embodiment of the present invention;

FIG. 22 is a schematic diagram of a physical structural configuration ofa heat exchanger network synthesis implementation for an industrialprocess according to an embodiment of the present invention;

FIG. 23 is a tabular description of an input file for a program fordetermining a heat exchanger network structure according to anembodiment of the present invention; and

FIG. 24 is a tabular description of an output file produced by a programfor determining heat exchanger network structure according to anembodiment of the present invention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, which illustrate embodiments ofthe invention. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theillustrated embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout. Prime notation, if used,indicates similar elements in alternative embodiments.

Many different types of processes consume multiple steam levels andelectricity to obtain an output result, or to produce a required productor compound. With large scale processes which consume significantamounts of steam, for example, it is preferable to optimize the steamand power system where possible. Heat exchanger network synthesis forwaste heat recovery under all possible combinations of processvariations is a very important sub-system in any new plant. Itssynthesis and design needs to be optimized during the design stage tominimize energy and capital costs and to make it 100% switchable to eachoperating mode and as flexible as economically feasible underdisturbances and uncertainty for its entire life cycle, as well as“easily-retrofitable” in future times due to dramatic changes in energyprices, new desirable operating modes, and/or new schemes of disturbanceand uncertainty. For example, in some industrial manufacturingprocesses, specific streams of material flows need to be supplied todifferent types of equipment and machinery at specific temperatures.These material flows may need to be heated or cooled from an originalstarting temperature to a target temperature. This, in turn, willrequire the consumption of steam to heat specific streams andconsumption of water, for example, to cool down specific streams undervarying process conditions.

From a switchability point of view, the new heat exchanger networkdesign may be required, for example, to face different operating modesto handle major changes in feed conditions such as crude oil type,natural gas flow, temperature, pressure and composition. It may also berequired to handle the processing of different products with differentspecifications as would be the case in the polymer industry (e.g.,different polymer grades), in the multi-product pharmaceuticalindustries, and in multi-feed, multi-product agriculture chemicalplants, and so on. In such situations, although the range of variationmight be significant, it is nevertheless necessary to design a heatexchanger network that can handle such situations all the time. In otherwords, the design should be feasible under all possible combinations andat each operating mode. Accordingly, in the case of switchability,decision-makers would not trade-off between network capital andoperating cost, but rather, would require that the design be sufficientto satisfy all operating modes.

From a flexibility point of view, however, the new heat exchangernetwork design can relax both the range of variations in the processconditions and the need for 100% feasibility. For example, in somecases, decision-makers can allow for a trade-off between the heatexchanger network capital cost and operating cost, on one hand, and theimpact on the rest of the process due less than 100% feasibility in thedesigned heat exchanger network under the given process variation range,on the other. It should be understood that the heat exchanger networkflexibility should provide for different small changes/disturbances anduncertainty due to, for example, ambient temperature changes, fouling inexchangers, catalyst deactivation, heat, mass and momentum transfercoefficients uncertainty, reaction kinetics parameters uncertainty(activation energy and frequency factor), equilibrium constantsuncertainty, degradation in equipment thermodynamic efficiency, and soon.

As such, according to various embodiments of the present invention,beneficially, these considerations can be taken into account during heatexchanger network synthesis and prior to detailed design. That is, it ispreferable to consider these important issues in heat exchanger networkdesign with a systematic method prior to the detailed design and actualconstruction of the physical plant and equipment. Correspondingly, wherethe state-of-the-art software in the market such as AspenTech Inc.product known as Aspen Pinch, and HX-NET, Pinch Express of KBC andSprint of UMIST, do not address the heat exchanger network life cycleswitchability and flexibility problems systematically, and inapplications of the near pinch and multiple pinches problems, render alarger number of units that necessary, various embodiments of thepresent invention advantageously overcome such limitations. Further,where such software that employs the pinch design approach in aniterative way, due to its nature, can not guarantee feasibility forswitchability purposes, can not systematically trade-off heat exchangernetwork flexibility versus the rest of the process, and can notoptimally select optimal or at least substantially optimal streamstarget temperatures under all possible combinations of the processvariations systematically, various embodiments of the present inventionadvantageously provide user friendly systematic methods, systems, andprogram product for heat exchanger network grassroots applications: thatrender heat exchanger network designs that have less than or equalnumber of heat exchanger units of the networks synthesized using otheriterative methods systematically and that, for all practical purposes,that render heat exchanger network designs that are guaranteed to beswitchable and have the right degree of flexibility for the heatexchanger network life cycle, and that render heat exchanger networkdesigns that exhibit easiness in its future retrofitability under allpossible combinations of process variations, and that provide anidentification of the heat exchanger network streams optimal targettemperatures for the respective network designs, all accomplishedwithout ad hoc iterations.

For a given list of process streams to be either cooled or heated withits interval heat capacity flow rate, interval supply and targettemperatures, set of stream-specific minimum approach temperatures, andinterval utilities targets that need to be satisfied or more or less tobe satisfied through bounded targets, various embodiments of themethods/techniques, systems, and program product can beneficially enablesynthesizing a heat exchanger network that sharply satisfies or more orless satisfies the interval utilities targets consumption within itsdefined bounds with less number of units, compared with pinch designmethod using advanced matching solutions, systematically, producing anetwork that exhibits heat exchanger network life cycle switchablity andflexiblity that is easily retrofitable in the future upon the change inenergy prices and/or disturbances and uncertainty schemes under allpossible combinations of process variations. Further, according touncertainty schemes where the process streams have desired targettemperatures in form of collapsed interval or as fixed numbers, variousembodiments of the methods/techniques, systems, and program product canbeneficially also select the optimal target temperature of each streamfrom within its given range.

FIGS. 1-24 provide examples illustrating various embodiments of methods,systems, and program product including algorithms to synthesize agrass-roots heat exchanger network and analyze a grass-roots heatexchanger network design, which can utilize targeting calculationsdescribed, for example, in one or more prior related patent/patentapplication disclosures identified at the end of this detaileddescription section, as an input file to the process steps and/oroperations described herein. Such targeting calculations data caninclude the global heating energy utility values (heating duty required)[Qh] and global cooling energy utility values (cooling duty required)[Qc] where the “[ ]” denotes interval values, as well as the location ofthe pinch region referred to as “region of minimum choice lower andupper temperature boundaries” shown in FIG. 4 at 103, 105, for example.Note, those skilled in the art should appreciate that variousembodiments of the present invention may encompass specific hardware orapparatus used to implement the present invention in addition to acomputer program product programmed into programmable logic or digitaldevices adapted to execute to a number of processing steps to achievethe aims of the invention.

Specifically, FIG. 1 illustrates a system 30 to determine global energyutility targets, to define an optimal driving force distribution,synthesize a grass-roots heat exchanger network, and analyze agrass-roots heat exchanger network design, for a process having aplurality of resource streams. The system 30 can include a heatexchanger network synthesizing computer 31 having a processor 33, memory35 coupled to the processor 33 to store software and database recordstherein, and a user interface 37 which can include a graphical display39 for displaying graphical images, and a user input device 41 as knownto those skilled in the art, to provide a user access to manipulate thesoftware and database records. Note, the computer 31 can be in the formof a personal computer or in the form of a server or server farm servingmultiple user interfaces 37 or other configuration known to thoseskilled in the art. Accordingly, the user interface 37 can be eitherdirectly connected to the computer 31 or through a network 38 as knownto those skilled in the art.

The system 30 can also include a database 43 stored in the memory 35(internal or external) of heat exchanger network synthesizing computer31 and having a plurality of sets of values each separately defining apotential range of values for at least one operational attribute foreach of a plurality of hot resource streams and a plurality of sets ofvalues each separately defining a potential range of values for at leastone operational attribute for each of a plurality of cold resourcestreams. Such attributes can include, for example, a lower and an upperboundary value for a supply temperature (Ts) of each of the hot resourcestreams and each of the cold resource streams, a lower and an upperboundary value for a target temperature (Tt) of each of the hot resourcestreams and each of the cold resource streams, and/or a lower and anupper boundary value for a heat capacity flow rate (FCp) of each of thehot resource streams and each of the cold resource streams, along withone or more sets of stream-specific minimum temperature approach valuesbetween streams (ΔTmin^(i)), streams initial types, streams matchingconstraints, and at least one interval global utility consumption value[Qh], [Qc], for the process according to the received streamsconditions.

The system 30 can also include heat exchanger network synthesizingprogram product 51 stored in memory 35 of the heat exchanger networksynthesizing computer 31 and adapted to provide systematic synthesis ofheat exchanger networks for switchability and flexibility under allpossible combinations of process variations in grassroots applicationswith easy-to-implement life-cycle retrofitability for a process orcluster of processes using a plurality of resource streams each havingoperational attributes including an interval heat capacity flow rate, adefined interval supply temperature, and a desired target temperaturethat can also be in interval form, accomplished without the need formanual (trial and error) enumeration, inherent in other prior systems.Note, the heat exchanger network synthesizing program product 51 can bein the form of microcode, programs, routines, and symbolic languagesthat provide a specific set for sets of ordered operations that controlthe functioning of the hardware and direct its operation, as known andunderstood by those skilled in the art. Note also, the heat exchangernetwork synthesizing program product 51, according to an embodiment ofthe present invention, need not reside in its entirety in volatilememory, but can be selectively loaded, as necessary, according tovarious methodologies as known and understood by those skilled in theart.

FIG. 2 illustrates a schematic graph illustrating a simple example of anindustrial process, overlaid upon successive temperature intervals 100generated therefor. The illustrated industrial process, providing whatis termed a “threshold problem” (i.e., one requiring only a cold or hotutility, but not both), incorporates four separate and distinct processstreams H1, H2, C1, C2, with H1, H2, and C1, having only discrete valuesfor the supply temperature and the target temperature, and H2, C1, andC2 having only discrete values for the heat capacity flow rate but withC2 having an interval value [115, 120] for its supply temperature and H1having an interval value [1.0, 1.8] for its heat capacity flow rate. Theresult is a network having a global cooling energy utility intervalvalue [Qc] of [10, 228] kW based upon a minimum temperature approachvalue (ΔT_(min)) of 10° K embedded in each hot stream H1, H2 and a heatexchanger duty (U) value of 0.1 for all heat exchangers. FIG. 3illustrates a schematic of the resulting heat exchanger network designfor the industrial process.

FIG. 4 illustrates a schematic graph illustrating a simple example of anindustrial process, overlaid upon successive temperature intervals 100generated therefor. The illustrated industrial process, providing whatis termed a “pinched problem” that needs both heating and coolingutilities, incorporates four separate and distinct process streams H1,H2, C1, C2, with H2 and C2, having only discrete values for the supplytemperature and the target temperature, and H1, H2, C1, and C2 havingonly discrete values for the heat capacity flow rate but with H1 havingan interval value [610, 630] for its supply temperature and an intervalvalue [260, 270] for its target temperature and C1 having an intervalvalue [150, 170] for its supply temperature and an interval value [400,420] for its target temperature. The result is a network having a globalcooling energy utility interval value [Qc] of [0.0, 40] kW and a globalheating energy utility interval value [Qh] of [260, 360] kW based upon aminimum temperature approach value (ΔT_(min)) of 10° K embedded in eachhot stream H1, H2 and a heat exchanger duty (U) value of 1.0 for allheat exchangers, with streams splitting of cold stream C2 beingperformed to enhance energy recovery through stream matching. FIG. 5illustrates a schematic of the resulting heat exchanger network designfor the industrial process.

The table below provides a high-level summary of a heat exchangernetwork design algorithm according to an example of an embodiment of thepresent invention:

Step # 0: Treat the problem as one problem without decomposition. Step #1: Receive attribute data for hot and cold streams of the process orprocesses. Step # 2: Calculate [Qh], [Qc], and find ROMC temperatureboundary. Generate temperature intervals having input variations in an,e.g., one-scale temperature interval diagram and apply specific minimumtemperature approach values. Step # 3: Match streams at each temperatureinterval for all types of problems moving from top-to-bottom (highest tolowest). Match streams that can cancel each other or one of them withminimum quality degradation to the other. Match streams with maximumoverlap or with equal or close to equal heat capacity flow rates (FCps).Match streams having high FCps and high heat transfer coefficients(“hi”) with streams having low FCps with low heat transfer coefficients.Employ stream switching/partial conversion, homogeneous matching, orbuffers (if feasible) to overcome non- thermodynamic constraints. Step #4: Target for utilities as guidance and balance loads using utilitiesduring step down through the temperature intervals. Step # 5: Splitstreams as necessary to reach the desired utilities loads and/or toreduce quality degradation. Step # 6: Determine an initial heatexchanger network design. Step # 7: Remove redundant process-to-processheat exchanger units. Step # 8: Merge same stream utility heat exchangerunits. Step # 9: Determine the final heat exchanger network design.

FIG. 6 provides a high-level flow diagram illustrating operation of theheat exchanger network synthesizing program product 51 and/or associatedmethod steps according to an embodiment of the present invention. Asshown in block 111, the program product 51 receives input data as aninput file (see, e.g., FIG. 11) which can include data indicatingpotential ranges of values for operational attributes for each of aplurality of process streams, a set {ΔT_(min) ^(i)[L:U]} of lower andupper stream-specific minimum temperature approach boundary valuesΔT_(min) ^(i) between streams, streams initial types, streams matchingconstraints, at least one interval global utility consumption value[Qh], [Qc], a location of lower and upper bounds of a pinch regionreferred to as “region of minimum choice” for the process according toreceived streams conditions provided, and indicia of a heat exchangernetwork design structure, for example, produced or otherwise determinedthrough application of an energy modeling process described, forexample, in addition detail, in U.S. patent application Ser. No.12/767,217, filed Apr. 26, 2010, titled “System, Method, and ProgramProduct for Synthesizing Non-Constrained and Constrained Heat ExchangerNetworks, and U.S. patent application Ser. No. 12/767,275, filed Apr.26, 2010, titled “System, Method, and Program Product for SynthesizingNon-Thermodynamically Constrained Heat Exchanger Networks,” incorporatedby reference in its entirety.

As shown in block 113, the program product 51 then calculates heatexchanger network design details to include a heat exchanger dutyinterval value [Q], hot streams supply temperature values [Ts], hotstream target temperature values [Tt], cold stream supply temperaturevalues' [ts], cold stream target temperature values [tt], and heatexchanger surface area “A” for each heat exchanger of the networkdesign, along with a corresponding total surface area, for the wholenetwork that satisfies the respective given/input process conditionvariations scheme. The table below provides a high-level summary of aheat exchanger network design details calculation algorithm according toan example of an embodiment of the present invention:

Step # 0: Treat ΔTmin¹ and realizing [Qc] and [Qh] as the mainconstraints to be satisfied. Step # 1: Use ΔTmin¹ check to decide pathforward for middle temperatures calculation. Step # 2: Ensure heatexchanger unit heat load Q realization and lower and upper boundscalculation using logic propagation. Step # 3: Use standard intervalmethod for middle temperatures and duties calculation for each heatexchanger unit heat load [Q]. Step # 4: Use modal intervals in case ofΔTmin¹ violation, or [Q]s constraints violation, or lower and upperbounds calculation logic constraints dissatisfaction.

Note, although the heat capacity flow rate FCp, supply temperature Ts,target temperature Tt, heat exchanger unit heat load Q, and heating andcooling energy Qh and Qc values are described as interval values where“[ ]” refers to interval values, one of ordinary skill in the art wouldunderstand that not all of such stream or heat exchanger operationattributes need be interval values. Rather, one or more or all can bediscreet point values. Regarding Step #1, the middle temperaturescalculation refers to the calculation of temperature between twoconsecutive units, such as, for example, [290; 310]° K for hot stream H1in FIG. 18. Regarding Step #2, logic propagation refers to maintainingthe heat balance of each stream intact, where a hot stream, for example,with known heat capacity flow rate [FCp] (or FCp) between a certainsupply temperature [Ts] (or Ts) and certain target temperature [Tt] andTt shall loose a certain [Q] (or Q). Regarding Step #3, the standardinterval method (for subtraction) refers to a method of obtaining aninterval answer that provides a worst-case scenario that may or may notbe realizable in some physical applications. For example, for thesubtraction of intervals [10; 15] and [5; 7], the result would be [3;10]: obtained by performing the following subtraction (10-7) and (15-5)to obtain the interval answer.

Regarding Step #4, the modal intervals calculation (for subtraction)refers to a method of obtaining a modal interval answer. For example,for the modal subtraction of intervals [10; 15] and [5; 7], the resultwould be [5; 8]: obtained by performing the following subtraction (10−5)and (15−7) to obtain the interval answer. The existence of a ΔTminviolation refers to the use of a value in any heat exchanger less thanthe one used in calculating the energy targets. The existence of a [Q]sviolation refers to a change in the heating utilities and coolingutilities interval energy targets calculated at certain global ΔTminused from the beginning in the energy targeting phase. Logic constraintsdissatisfaction refers to a situation where when subtracting intervals,we find that the cold stream at higher temperature than the hot streamis exchanging heat in one or more of the designed heat exchanger units.

According to an embodiment of the present invention, the surface areathat satisfies desired process variations possibility schemes can be themaximum one obtained through use of a heat exchanger-by-heat exchangeralgebraically calculation to find the required maximum realizable area“A” using, for example, the overall heat transfer coefficient U andmaximum realizable heat exchanger duty Q over log mean temperaturedifference ΔT_LMTD, using an algebraic formula such as, for example,that described below and illustrated in FIGS. 7A-12, and/or using a heatexchanger device optimization algorithm that repeatedly solves amathematical program with variable objective illustrated in FIG. 21 anddescribed in more detail later.

The algebraic formula according to the first of the two configurationsidentified above, is as follows:

Max A=Max Q/U*ΔT_LMTD,

wherein:

-   -   Q=FCp*(Ts-Tt)=fcp*(tt-ts),    -   y1>=ΔT_min,    -   y2>=ΔT_min,    -   y1=Tt-ts,    -   y2=Ts-tt,    -   ΔT_LMTD={y1*y2*(y1+y2)/2}**0.333333,    -   [FCp]=[FCp_(—1;FCp)_U],    -   [fcp]=[fcp_L;fcp_U],    -   [Ts]=[Ts_L;Ts_U],    -   [Tt]=[Tt_L;Tt_U],    -   [ts]=[ts_L; ts_U],    -   [tt]=[tt_L; tt_U],    -   Q<=Q_U,    -   Q>=Q_L, and    -   U=1.0.

The following table provides additional abbreviations:

FCp: Heat capacity flow rate of a hot or cold stream [FCp1h]: IntervalHeat capacity flow rate of hot stream # 1 [FCp1c]: Interval Heatcapacity flow rate of cold stream #1 MM Million British thermal unitsper hour. Degree Btu/h. °F.: Qc: Cooling duty required Qh: Heating dutyrequired [Qc]: Interval cooling duty required [Qh]: Interval heatingduty required kW: Kilo watts kW/° K: Kilo watts per degree KelvinΔT_min: Minimum approach temperature HEN: Heat exchanger network hi:Stream heat transfer coefficient U: Overall heat transfer coefficient A:Heat exchanger surface area h: Hot stream c: Cold stream T_LMTD: Logmean temperature difference U_l: Lower bound of overall heat transfercoefficient Q_U: Upper bound of heat exchanger duty Ts_l: Lower bound ofhot stream supply temperature Ts_U: Upper bound of hot stream supplytemperature Tt_l: Lower bound of hot stream target temperature Tt_U:Upper bound of hot stream target temperature ts_l: Lower bound of coldstream supply temperature ts_U: Upper bound of cold stream supplytemperature tt_l: Lower bound of cold stream target temperature tt_U:Upper bound of cold stream target temperature Ts: Stream supplytemperature [Ts]: Interval stream supply temperature Tt: Stream targettemperature [Tt]: Interval stream target temperature [Q]: Interval heatexchanger duty required

FIG. 7A illustrates a single heat exchanger having an interval hotstream supply temperature [Ts], an interval hot stream targettemperature [Tt], an interval cold stream supply temperature [ts], aninterval cold stream target temperature [tt], and an interval heatexchanger duty [Q] having a overall heat transfer coefficient U equal to1.0. FIG. 7B illustrates a relative difference between streamtemperatures. FIG. 8 provides a graphical representation of the singleheat exchanger having input data used for an input file such as, forexample, the file graphically illustrated in FIG. 11. According to anembodiment of the systems, methods, and program product 51, theassociated steps/operations include receiving the input file, internallyconstructing a heat exchanger node shown in FIG. 8, determining theinterval heat exchanger duty [Q] and the interval heat exchanger surfacearea [A] as is graphically displayed in FIG. 9, and selecting themaximum of the interval heat exchanger duty [Q] as is graphicallydisplayed in FIG. 10, which in this example, renders a value of 32 m².Finally, the steps/operations also include outputting an output file,such as, for example, the file graphically illustrated in FIG. 12.

Disturbance & Uncertainty Schemes Representation and Optimal HeatExchanger Network Design and Flexibility Level

An exemplary embodiment of the present invention provides for thedevelopment and analysis of possibility schemes for switchability andflexibility variations, adapting Nested Intervals representationtechniques. A hot stream supply temperature (Th1) can, for example, havethe possibility of being equal to [150, 160]° K 100% of the time, [145,170]° K 98% of the time, [142, 175]° K 95% of the time, and [140, 180]°K 90% of the time in a nested interval form. According to an exemplaryconfiguration, feasibility for switchability can be achieved with aminimum number of heat exchanger units and minimum energy consumption ina heat exchanger network design to satisfy process switchability needsfor the given ranges of variations of 100% possibility of time. Note, aprocess stream having operational attribute values of “100% possibilityof time” refers to the respective value being equal to a given range100% of the time. The 100% possibility range on a variable is the rangewith highest possible confidence. In other words, the 100% possibilitymeans that 100% the operating time of the plant, the plant will be inthat range—[150, 160]° K in this illustrative example. In practice, thesummer and winter conditions of a gas stream inlet temperature normallyis rigorously known. Also, different crudes have known specificgravities, etc. Other ranges with less confidence, e.g., 98% of theoperating time and so on represent an outer value range of the mostassured one in the core, which sits or is otherwise nested within the98% range. In Switchability applications, according to an embodiment ofthe present invention, it is preferred that one uses the 100% confidencerange, for example, to design the heat exchanger network, e.g., withoutchecking the operating and fixed cost of the network.

According to an exemplary configuration, feasibility for flexibility for100% process variations possibility of the time, however, is notmandatory. In such flexibility applications, the representation again isin a nested form with percentage for each possibility range operatingtime of the plant, but the order of the process variation ranges isreversed as compared with that for switchability. That is, the widestrange of the variable(s) interval represent the 100% flexibility suchthat if the heat exchanger network is going to be designed for thisvariation range for each variable, it will be 100% feasible at the worstcase scenario with ultimate confidence that process changes will neverbecome outside these intervals. With tighter (narrower) ranges onprocess variable(s), flexibility goes down as does the cost of bothenergy consumption and heat exchanger network capital cost, but theimpact of streams target temperature not reaching the desired value(s)in case of wider range of disturbance affecting the downstream units inthe plant such as reactors and distillation columns and so on, can havea substantial cost sufficient to warrant a search for optimalflexibility level according to various embodiments the presentinvention.

According to an embodiment of the present invention, the desired levelof flexibility can be determined using a process performanceformula/algorithm to analyze an economic trade-off between feasibilityfor flexibility for given ranges of variation through comparison ofannualized fixed and operating costs for a given heat exchanger networkdesign in view of a cost impact on process economics due to the lack offlexibility in one or more target temperature fluctuation for a specific“possibility” time. For example, each stream specific target temperatureTt_(i) can be determined/analyzed for comparative purposes as a functionof product yield, product quality, and production cost, i.e., f(productyield, product quality, production cost) where cost impact or profit ($)equals α+bT_(ti) ^(n).

FIG. 13 illustrates a simple high-level flow diagram for determining aneconomic trade-off between heat exchanger network capital and energycost and impact on process economics to select an optimal heat exchangernetwork design and for determining and using different levels offeasibility for given variations and their associated possibility timesto find an optimal flexibility level, according to an exemplaryembodiment of the present invention. The steps/operations can includedetermining a heat exchanger network design for each different one ofmultiple process variation schemes according to a corresponding multipletime possibilities/probabilities (block 121), and determining thecapital and operating costs for each of the heat exchanger networkdesigns (block 123). Beneficially, as described in more detail below,the operating costs can be used in analyzing a trade-off with the fixedcosts of the heat exchanger network based, for example, upon a ΔTmin^(i)set selection in evaluating the energy cost at each process variationsschemes at different possibility levels as well as in calculatingflexibility level upon considering the cost impact of differentflexibility levels on other process units and its economics.

The heat exchanger network designs can be produced via energy modelingas described previously. Additionally, using, for example, the intervalcollapsing algorithm described in U.S. patent application Ser. No.12/715,255, filed Mar. 1, 2010, titled “System, Method, and ProgramProduct for Targeting and Optimal Driving Force Distribution in EnergyRecovery Systems,” the energy operating costs can be determined usingthe interval heating and cooling duties [Qh] and [Qc] for each of theheat exchanger network designs to calculate the average realizablemaximum energy cost and average realizable minimum energy cost undereach interval possibility scheme to obtain a best estimate for energyoperating cost. Since each scenario can be assumed to have a possibilityof 50%, Shanon's Maximum Entropy Concept, for example, can then be usedto estimate energy operating cost through calculating the average ofboth maximum energy cost and minimum energy cost under each intervalpossibility distribution scheme.

The table below provides a summary of the energy operating costestimation algorithm according to an example of an embodiment of thepresent invention:

Step # 1: Find the best case scenario energy cost via calculating theglobal minimum heating duty Qh and corresponding cooling duty Qc, andglobal minimum cooling duty Qc and corresponding heating duty Qh. Step #2: Find the worst case scenario energy cost via calculating the globalmaximum heating duty Qh and corresponding cooling duty Qc, and globalmaximum cooling duty Qc and corresponding heating duty Qh. Step # 3:Employ Shanon's Maximum Entropy Concept to estimate energy operatingcost through getting the average of both maximum energy cost and minimumenergy cost under each interval possibility distribution scheme.

In order for a designed network to reach the desired hot stream targettemperature Thi with 100% possibility of the time a cost-1 will need tobe incurred, for 98% possibility of the time a cost-2 will need to beincurred, for 95% possibility of the time a cost-3 will need to beincurred, and for 90% possibility of time a cost-4 will need to beincurred, and so on. Accordingly, the steps/operations can also includeapplying at least one, but more typically each of the supply temperatureand/or heat capacity flow rate range of values for each of the processstreams for a heat exchanger network designed for 100% processvariations, for example, one at a time, to corresponding process streamsfor each of the other heat networks designed having lesser timepossibility of process variations (block 130) to determine aprocess-cost-impact of utilizing the different network designs. Moreparticularly, the step/operation of applying supply temperature and/orheat capacity flow rate values can include assigning the design processstream supply temperatures and/or heat capacity flow rate of one of theprocess streams of network designed for 100% process variation to acorresponding process stream of one of the heat exchanger networks(under evaluation) designed for a lesser percentage (block 131),analyzing the process-cost-impact of an associated change in targettemperature for the process stream and on other process streams on thenetwork design under evaluation (block 133), and repeating the“applying” step until all process streams in the network design underevaluation have been evaluated (block 135). The steps/operations canfurther include repeating the step of applying the 100% supplytemperature and/or heat capacity flow rate values until all othernetworks designed for a lesser percentage of process variations havebeen evaluated (block 141), and determining the optimal heat exchangernetwork design and system-level optimal flexibility index, as a resultof such evaluations (block 143). The steps/operations can also includedetermining a flexibility priority list that can include differentflexibility levels for each individual process stream target temperature(stream-specific flexibility level) (block 145), and a correspondingcriticality list for process streams supply attributes variations, e.g.,due to disturbances and/or uncertainty of each process streams supplytemperatures (Ts) and/or heat capacity flow rates (FCp) (block 147).

As described above, for switchability, a 100% possibility is required.In other words, according to a preferred configuration, 100% feasibilityis normally needed to accommodate different operating modes. Forflexibility levels determination, however, the cost calculation atdifferent possibilities of time can be used for the triple trade-offamong energy cost, annualized heat exchanger network capital cost, andeconomic impact on the process.

For example, consider the below methodology to perform the flexibilitylevel economic calculation that enables one to identify an optimalflexibility level for each stream target temperature of eachcorresponding stream of a process assumed to be something less than 100%in the face of a given small range of disturbances and uncertainties ininput variables, using Thi target temperature. First, one can use theabove described methods to design a feasible heat exchanger network for90% process variation range and apply on it the 100% range of variationof the low disturbances/uncertainty kind to analyze that affect offlexibility on the heat exchanger network. Such test will result in aThi target temperature equal to value “[X]”° F., for example, that isnot exactly the range desired by the process. Using these sub-optimalvalues, one can determine the cost impact of such deviation/change inthis target temperature (i.e., for a possibility of 10% of the time) onthe economics of the rest of process units (“process-impact-cost”).

Next, the heat exchanger network capital and energy operating costsdesigned for 100% process variations are compared with suchprocess-cost-impact. Finally, in order to complete the analysis, thesuboptimal target temperature range (Thi) can be used to determine theeconomic impact on both heat exchanger network capital and energyoperating cost for each process stream target temperature, one-by-onestream, to allow for differentiating among heat exchanger network targettemperatures priority by its economic impact on the rest of the processunits.

Beneficially, such differentiation can result in creation of thestream-specific-flexibility-level concept. Further, beneficially, thisapproach facilitates the identification of the right (optimal) trade-offbetween the heat exchanger network capital and energy cost on the onehand and the impact on the rest of process economics due to lack of heatexchanger network flexibility (i.e. for 10% of the time) on the otherhand. Still further, beneficially, depending upon the results of thecomparison, this evaluation may show that 90% of flexibility in thistarget temperature may not have an economic impact on the process thatjustifies the potential extra cost of both heat exchanger networkcapital and energy needed to achieve 100% flexibility.

In summary, the exemplary embodiment of the present invention includesprocedures to find optimal flexibility level for the whole system (i.e.,same flexibility level across all process streams) and an optimalflexibility level for each target temperature through calculating itsimpact on process economics versus its impact on heat exchanger networkcapital and energy costs, and procedures to find optimal targettemperatures ranges from streams data for a heat exchanger networkworking with different time possibilities according to the variationsschemes available, for example, for possibility of 80%, 90%, 95% and100% of time. The procedures provide the ability to then check, forexample, the network designed for 90% possibility of the timedisturbance scheme working under 100% variation and to find thecorresponding target temperatures range of each target temperature Tt inthe target temperature set TtI. If the difference in capital cost andoperating cost of the two heat exchanger network designs (e.g., the onedesigned for 100% variation and the one designed for 90% variation) ishigher than the impact of the target temperatures deviation on theprocess economics, then the heat exchanger network designed for 90%possibility time is the more optimal between the two designs and theassociated variation scheme represents the optimal flexibility index ofthe heat exchanger network. The exemplary embodiment of the presentinvention also utilizes the above described process steps to form astream-specific target temperature flexibility priority list and acorresponding supply attributes variations criticality list. Thestream-specific target temperature flexibility priority list can includedifferent stream-specific flexibility levels for each individual processstream target temperature obtained through application of each separateflexibility level to the same set of process streams. The supplyattributes variations criticality list can include critical values forthe process streams supply temperatures (Ts) and heat capacity flowrates (FCp) determined through an analysis of the effect of thedeviation in target temperature range of variation for one or more ofthe process streams for a heat exchanger network design formed accordingto a first process variation scheme responsive to application of asupply attribute value range of variation (e.g., interval values forsupply temperature and/or heat capacity flow rate) according to adifferent process variation scheme, to the corresponding supplyattribute (e.g., supply temperature or the capacity flow rate) of theone or more process streams for the heat exchanger network design—e.g.,through analysis of the outcome of replacing the attribute values of aprocess variation scheme used to design the heat exchanger network withattribute values of a process variation scheme having a different levelof flexibility.

Optimal Target Temperatures Selection

Various embodiments of the present invention includeprocesses/algorithms for selecting an optimal target temperature from atarget temperature range under all possible combinations of variationsin other variables during the design phase. FIG. 14, for example,provides a high-level flow diagram illustrating operations of the heatexchanger network synthesizing program product 51 and/or associatedmethod steps according to an embodiment of the present invention, whichprovide a methodology for systematically determining optimal targettemperatures under all given disturbance ranges in input conditions froman energy cost point of view from within a given range by utilizing anoptimization process which, itself, can utilize the interval collapsingalgorithm identified previously.

According to the exemplary implementation illustrated in FIG. 14, theoperation/steps include first retrieving or otherwise receiving,identifying, or generating a lower and an upper boundary value for atarget temperature defining a target temperature range interval for eachseparate one of a plurality of process streams that substantiallyidentify all anticipated possible combinations of substantial variationsof target temperature for the process (block 151). For simplicity, thedecision maker can assign, for example, a range of ±5-10° F. whenanticipated temperature variations are fairly well-known, ±10% when lesswell-known, or some other value which encompasses current and/or futureuncertainty, around each target temperature for each process stream. Thesteps/operations can also include determining a plurality of temperaturestep intervals (block 153) as described, for example, in U.S. patentapplication Ser. No. 12/715,255, filed Mar. 1, 2010, titled “System,Method, and Program Product for Targeting and Optimal Driving ForceDistribution in Energy Recovery Systems,” whereby each temperature stepinterval includes an input interval indicating heat extractedcollectively from the plurality of hot process streams, an outputinterval indicating heat collectively applied to the plurality of coldprocess streams, and an output interval indicating surplus heatavailable for a next of the plurality of temperature step intervals,which can be useful in determining the heating duty [Qh] and the coolingduty [Qc] for the process.

The steps/operations can also include performing an economic evaluationon target temperature of the process streams of the process (block 160)to include both hot process streams and cold process streams accordingto this exemplary embodiment of the method/program product. Thisstep/operation can be performed, for example, by collapsing the targettemperature step interval for the process streams under evaluation onits vertices to render the discrete target temperature boundary values,with the target temperature range interval for each other of the processstreams remaining in interval form (block 161), and identifying thetarget temperature value rendering a global minimum of a desired energyutility target (block 162). Note, according to this exemplaryconfiguration, if neither of the boundary temperature interval valuesprovide the global minimum heating or global minimum cooling valuescalculated before collapsing the interval, as may be expected when thepinch point location changes, the process then further steps through thetemperatures within the interval, degree-by-degree. In an alternativeconfiguration, the process performs the degree-by-degree analysiswithout first analyzing or comparing the global minimum values obtainedfrom the discrete temperature boundary values with those obtained priorto collapsing the respective interval.

The steps/operations can also include synthesizing a heat exchangernetwork “design” responsive to the identified target temperature value(block 163), calculating, e.g., annualized capital costs associated withthe synthesized heat exchanger network (block 164), calculating, e.g.,annualized operating costs associated with the synthesized heatexchanger network (block 165), and calculating, e.g., annualizedprocess-impact-costs of a deviation in the respective target temperaturerange interval for the respective process stream under evaluation onprocess economics associated with the synthesized heat exchanger networkfor other portions of the process—e.g., costs resulting from thesub-optimal target temperature interval (block 166).

The steps/operations can also include repeating the step of performingan economic evaluation on target temperature for each other of theprocess streams (block 171), and selecting an optimal stream-specificset of target temperature values {Tt_(i)} rendering an optimal heatexchanger network design responsive to the economic evaluation on targettemperature for each of the process streams (block 173)—i.e., responsiveto the impact of the deviation in target temperature range on processeconomics, energy consumption, and switchable and flexible heatexchanger network capital cost. In essence, the exemplary evaluationprocess beneficially allows for differentiating between targettemperatures Tt_(i) through their individual economic impact on the restof the process units.

Grass-Roots Design of Optimal Topology for Future Retrofit

Various embodiments of the present invention provide systems, programproduct, and methods of synthesizing an, e.g., grass-roots, heatexchanger network for an industrial process including multiple hotprocess streams to be cooled and multiple cold process streams to beheated, and various hot and/or cold utilities to supplement the wasteheat recovery system, which satisfy the life cycle switchability andflexibility concepts of the synthesized heat exchanger network,described above, for both current and future conditions. That is,various embodiments of the present invention provide systems, methods,and program product for synthesizing heat exchanger networks designed tominimize energy consumption, structured to satisfy current needs: toaccommodate future changes in energy costs under current disturbancesand uncertainty schemes; and to accommodate future time-dependant newoperating modes, disturbances, and uncertainty schemes.

The table below provides a high-level summary of a heat exchangernetwork synthesis algorithm according to an embodiment of the presentinvention, which produces heat exchanger network structures specificallyconfigured for future retrofit under current disturbances anduncertainty schemes to accommodate future changes in energy costs underthe current disturbances and uncertainty schemes:

Step # 1: Start heat exchanger network (HEN) synthesis using highminimum temperature approach value or set of values. Step # 2:Synthesize several HENs at sequentially lower minimum temperatureapproach values using a systematic method. Step # 3: Produce HENs thatare all exhibiting the same structure/ topology and differ only in loadallocation on each heat exchanger (heat exchanger duty or heat transferbetween streams) and the possibility of adding additional heat exchangerunits and/or bypassing excess heat exchanger units, partially and/orcompletely. Step # 4: Select the network that satisfies current economiccriteria and keep other designs for future retrofit upon the change inthe trade-off between energy cost and capital cost that keep currentnetwork operability intact. Step # 5: Reserve in the plant layoutsufficient free space for the specific heat exchangers that will requireextra surface area in the future due to anticipated possible increasedload.

Steps 1-3: The steps of synthesizing a grassroots heat exchanger networkfor future retrofit, according to an example of an embodiment of thepresent invention, by synthesizing several grass-roots heat exchangernetwork designs at sequentially lower minimum temperature approachvalues ΔT_(min) ^(i) beginning at a high (“maximum”) minimum temperatureapproach value (or set of values) using a systematic method inaccordance with steps 1-3, are shown, for example, in FIGS. 15-17. Thatis, the exemplary implementation shown in FIGS. 15-17 illustrates anexample of a step-by-step synthesis of agrassroots-design-for-future-retrofit to include an illustration of howapplication of sets of successively different (e.g, lower)stream-specific minimum temperature approach values ΔT_(min) ^(i) foreach hot process stream, beginning, for example, at the highest minimumtemperature approach values (e.g., 30° K. in this example), followed bysuccessively lower minimum temperature approach values (e.g., 20° K. and10° K. in this example for simplicity), can yield a series of heatexchanger network configurations having common network structures, butwith the possibility of having successively fewer numbers of heatexchanger units, which can readily be used to facilitate construction ona heat exchanger network that has a topology that is easilyretrofittable based on possible future differing load requirements.Note, although the exemplary process configuration features beginning ata maximum temperature approach value or set of values, embodiments wherea minimum temperature approach value or values are used to begin theanalysis, or where intermediate values are used first, are within thescope of the present invention.

Beneficially, the results of steps 2 and 3 provide a continuum of userselectable heat exchanger network designs extending, for example,between (1) a heat exchanger network design having hot streams assigneda set of minimum temperature approach values {ΔT_(min) ^(i)} establishedat a corresponding set of expected maximum values, generally resultingin a most heat exchanger populated heat exchanger network design due tothe need for utilities (heaters and coolers), and (2) a heat exchangernetwork design having hot streams assigned a set of minimum temperatureapproach values {ΔT_(min) ^(i)} established at a corresponding set ofexpected minimum values, generally resulting in a least heat exchangerpopulated heat exchanger network design due to a lesser requirement forutilities (heaters and/or coolers) but with heat exchanger units thatgenerally require more surface area “A” and other capital investment.Further beneficially, the most heat exchanger populated heat exchangernetwork design can be used to identify the maximum amount of real estateneeded for providing necessary hot and cold utilities streams and hotand cold utilities heat exchangers; and the least heat exchangerpopulated heat exchanger network design can be used to identify themaximum amount of real estate necessary for retrofitting or otherwiseproviding heat exchangers for delivering a maximum design required loador heat transfer requirement. Note, for a detailed discussion ofimplementation examples illustrating steps 2-3, see U.S. patentapplication Ser. No. 12/767,315, filed Apr. 26, 2010, titled “System,Method, and Program Product for Synthesizing Heat Exchanger Networks andIdentifying Optimal Topology for Future Retrofit.”

Step 4: Step 4 includes selection of a network from within the continuumof user selectable heat exchanger network designs that satisfies currenteconomic criteria such as, for example, the trade-off between capitalcosts/investment and the current and forecast cost of heating or coolingutilities. The step can also include maintaining the heat exchangernetwork designs within the continuum that were not selected to providethe blueprint for a future retrofit upon the change in the trade-offbetween energy cost and capital cost.

Step 5: Step 5 applies to an initial build/development of the industrialprocess facility or a current retrofit. Specifically, step 5 includesreserving in the plant layout sufficient free space for the specificheat exchangers that will require extra surface area in the future dueto anticipated possible increased load, for example, due to a sufficientincrease in the cost of heating, cooling, or heating and coolingutilities, depending upon that utilized and/or required according to thecurrent network design and according to that which would be requiredaccording to the higher-load, reduced-utility retrofit design.Optionally and/or alternatively, step 5 can also include reserving inthe plant layout sufficient free space for the addition of additionalutilities such as, for example, due to a sufficient decrease in the costof heating, cooling, or heating and cooling utilities, in conjunctionwith a requirement to replace one or more heat exchanger units, such as,for example, due to damage or age, again, depending upon that utilizedand/or required according to the current network design and according tothat which would be required according to the lower-load,increased-utility retrofit design.

Various embodiments of the present invention provide systems, methods,and program product for synthesizing heat exchanger networks designed toaccommodate future time-dependant new operating modes, disturbances, anduncertainty schemes (e.g., gas-oil-ratio percentage water cut, etc.). Byway of example, the table below provides a high-level summary of a heatexchanger network synthesis algorithm according to an embodiment of thepresent invention, which produces heat exchanger network structuresspecifically configured for future retrofit under future time-dependantnew operating modes, disturbances, and uncertainty schemes:

Step # 1: Start heat exchanger network (HEN) synthesis for an expectedfuture high range of disturbances and uncertainty scheme. Step # 2:Synthesize several HENs at sequentially lower ranges that match currentand future short-term needs. Step # 3: Produce HENs that are allexhibiting the same structure/ topology and differ only in loadallocation on each heat exchanger (heat exchanger duty or heat transferbetween streams) and the possibility of adding additional heat exchangerunits and/or bypassing excess heat exchanger units, partially and/orcompletely. Step # 4: Select the network that satisfies currenteconomic, switchability, and flexibility criteria and keep other designsfor future retrofit that accommodate new switchability and flexibilityneeds without major modifications. Step # 5: Reserve in the plant layoutsufficient free space for the specific heat exchangers that will requireextra surface area in the future due to anticipated possible newswitchability and flexibility needs.

Steps 1-3: The steps of synthesizing a grassroots heat exchanger networkfor future retrofit, according to an example of an embodiment of thepresent invention, by synthesizing several grass-roots heat exchangernetwork designs at sequentially lower ranges of supply temperaturevalues, heat capacity flow rate values, and/or target temperature valuesfor the process streams of a process beginning with a process variationscheme at a high (“maximum”) expected range of values (or set of values)using a systematic method in accordance with steps 1-3 are shown, forexample, in FIGS. 18-20. That is, the exemplary implementation shown inFIGS. 18-20 illustrates an example of a step-by-step synthesis of agrassroots-design-for-future-retrofit to include an illustration of howapplication of sets of successively different supply temperature rangevalues of certain process streams, beginning, for example, at the, e.g.,highest (widest) range values followed by successively lower (narrower)range values, can yield a series of heat exchanger networkconfigurations having common network structures, but with thepossibility of having successively fewer numbers of heat exchangerunits, which can be used to facilitate construction on a heat exchangernetwork that has a topology that is easily retrofittable based onpossible future differing load requirements. Note, although theexemplary configuration features beginning at a maximum range of valuesor set of values, embodiments where a minimum range of values or valuesare used to begin the analysis, or where an intermediate range of valuesor sets of values are used to begin the analysis, are within the scopeof the present invention.

Beneficially, the results of steps 2 and 3 provide a continuum of userselectable heat exchanger network designs extending, for example,between: (1) a heat exchanger network design having process streamsassigned a set of supply temperatures and/or heat capacity flow ratesestablished at a corresponding set of expected maximum range values,generally resulting in a most heat exchanger populated heat exchangernetwork design due to the need for utilities (heaters and coolers), and(2) a heat exchanger network design having hot streams assigned a set ofsupply and/or target temperatures established at a corresponding set ofexpected minimum range values, generally resulting in a least heatexchanger populated heat exchanger network design due to a lesserrequirement for utilities (heaters and/or coolers) but with heatexchanger units that generally require more surface area and othercapital investment. Further beneficially, the most heat exchangerpopulated heat exchanger network design (typically requiring lesssurface area per heat exchanger units) can be used to identify themaximum amount of real estate necessary for providing the additionalnecessary hot and cold utilities streams and hot and cold utilities heatexchangers. Correspondingly, the least heat exchanger populated heatexchanger network design can be used to identify the maximum amount ofreal estate (e.g., room accommodate increased heat exchanger surfacearea) necessary for retrofitting existing heat exchangers or providingreplacement heat exchangers for delivering a maximum design requiredload or heat transfer requirement.

Step 4: Step 4 includes selection of a network from within the continuumof user selectable heat exchanger network designs that satisfies currenteconomic and operability criteria such as, for example, the trade-offbetween capital costs/investment, the current and forecast cost ofheating or cooling utilities, and the process-cost-impact of currentdisturbances and uncertainty. The step can also include maintaining theheat exchanger network designs within the continuum that were notselected to provide the blueprint for a future retrofit upon the changein the trade-off between energy cost and capital cost and new (future)operating modes, disturbances, and uncertainty schemes, which could beimplemented without major modifications. Major modifications generallyinclude topological modifications that are undoable due to lack ofspace, need an interruption of the plant operation and/or extremelyexpensive to implement. For example, major modifications can includemoving a heat exchanger and/or associated components from one locationto another to change the sequence of the units. Major modifications canalso include the need of re-matching of streams and changing the serviceof a heat exchanger. Major modifications can further include the need toadd multiple new heat exchanger units in a limited space, and/or addinga bypass where there is no space available for piping.

Step 5: Step 5 applies to an initial build/development of the industrialprocess facility or a current retrofit. Specifically, step 5 includesreserving (in the plant layout) sufficient free space for the specificheat exchangers that will require extra surface area in the future dueto an anticipated possible increased load, for example, due to asufficient increase in uncertainty and/or disturbances and/or newoperating mode requirements, etc., depending upon that utilized and/orrequired according to the current network design and according to thatwhich would be required according to the higher-load, reduced-utilityretrofit design. Optionally and/or alternatively, step 5 can alsoinclude reserving (in the plant layout) sufficient free space for theaddition of additional utilities such as, for example, due to asufficient decrease in uncertainty and/or disturbances and/or reducedrequirements of a new operating mode, in conjunction with or alternativeto a requirement to replace one or more heat exchanger units, such as,for example, due to damage or age, again, depending upon that utilizedand/or required according to the current network design and according tothat which would be required according to the lower-load,increased-utility retrofit design.

Automated Generation of Detailed Design of Synthesized Heat ExchangerNetwork

Various embodiments of the present invention include an algorithm thatrepeatedly solves a mathematical program MP with variable objective todetermine heat exchanger area and duty intervals and branch flow rateand temperature intervals. The mathematical program is denoted MP and isdefined over the sets and parameters that define the HEN. The objectiveof the mathematical program includes a variable input denoted by OBJ,and it returns the following sets of variables that best meet theobjective OBJ: (a) process-to-process heat exchanger duty, overall heattransfer coefficient, surface area, inlet temperature for the hot andcold sides, and the outlet temperature for the hot and cold sides; (b)utility heat exchanger surface areas, utility temperatures, overall heattransfer coefficient temperatures, and heating or cooling duties; and(c) network branch temperatures and flow rates.

FIG. 21 illustrates the steps/operations employed by a surface areadetermination algorithm, according to an embodiment of the presentinvention, employed as part of program product 51 or as a stand-alonemodule, as be understood by those of ordinary skill in the art. Thesteps/operations of such algorithm include, for example, retrieving orotherwise receiving input data defining the process stream, heatexchanger, and network connectivity attributes that define the structureof a heat exchanger network 191 (block 201) such as, for example, thatshown in the FIG. 22, and generating an input file from the input data(block 203) such as, for example, that shown in FIG. 23. The input datacan include process stream attributes including process stream names andtheir respective starting temperature ranges, target temperature ranges,flow rate ranges, and specific heat ranges; process-to-process heatexchanger attributes including the heat exchanger names and theirrespective minimum approach temperatures and overall heat transfercoefficient ranges; utility heat exchanger attributes including utilityexchanger names and their respective type (heating or cooling utilityexchanger), minimum approach temperatures, utility temperature ranges,overall heat transfer coefficient ranges, and heating or cooling dutytemperature ranges; and network connectivity attributes specified bydefining the branches in the network that connect the different elementsof the network to include: (a) nodes comprising either a stream'sstarting terminal, a stream's ending terminal, the hot side of aprocess-to-process heat exchanger, the cold side of a process-to-processheat exchanger, or a utility exchanger; and (b) branches each defined byits stream, source node, and target node. Correspondingly, the inputfile can provide parameters in both discrete and interval form thatdefine the network to be used by the mathematical program.

The steps/operations can also include defining inputs (string options)for an objective iterations string function used to generate anobjective function OBJ (block 205). According to the exemplaryconfiguration, the objective function string is composed of threeinputs: (a) the optimization option OPT describing the two-optimizationoption (minimize or maximize); (b) the attribute ATT being optimizeddescribing the eight attributes to be optimized, which correspond tobranch flows and temperatures in the network, heat exchanger input andoutput temperatures, process-to-process heat exchanger duties and areas,and utility heat exchanger duties and areas; and (c) the heat exchangernetwork element index nATT that the attribute is defined over describingthe number of elements for each attribute which is used to select theheat exchanger network element index.

The steps/operations can also include assigning the variable i as inindex to iterate over OPT and initializing it to 1 (block 207),assigning the variable j as in index to iterate over ATT andinitializing it to 1 (block 209), assigning the variable k as in indexto iterate over nATT and initializing it to 1 (block 211), determiningthe objective string OBJ by concatenating OPT, ATT, and k into a singlestring using the following formula: OBJ=Concentrate(OPT[

],AFF[

], “[”,k, “]”) (block 213), and solving the mathematical program MPusing the HEN input file and the OBJ objective and storing the result inthe RES file (block 215). Note, this step is denoted byRES=MP(HBN,OBJ]in FIG. 21.

The steps/operations can also include storing the objective value of theproblem as a bound to the variable in the objective (block 217). Note,if OPT[i] is “max,” then the objective is an upper bound. Otherwise, itis a lower bound. The variable is the attribute ATT[j] of the HENelement k. This step is denoted by ATT[j][k]_OFF[

]=RES[Objective Value] in FIG. 21. The steps/operations can also includeincrementing the counter k by 1 after storing the objective value (block219), and determining if k is no greater than the number of elementsthat has the attribute ATT[j] (i.e. if k≦nATT[j]) (block 221). If so,the process returns to block 213, otherwise the process continues byincrementing the counter j by 1 (block 223) and determining whether eachof the eight attributes have been returned by the mathematical program(block 225). If j is no greater than the number of attributes beingconsidered, which is 8, (i.e. if j≦8) then the process returns to block211, otherwise the process continues by incrementing the counter i by 1(block 227) and determining if both optimization objective options havebeen addressed (block 229). If i is no greater than the number ofoptimization objective options being considered, which is 2, (i.e. ifi≦2) then the process returns to block 209, otherwise the programterminates the process.

Mathematical Program (MP) Formulation

According to an exemplary embodiment of the present invention, themathematical program (MP) takes two types of inputs: the sets andparameters that define the heat exchanger network, shown below, and theobjective function OBJ. The problem then returns the objectivefunction's value and the variables defined below (e.g., thetemperatures, flows, duties, and surface areas of different componentsin the HEN) that best satisfy the objective function. The sets andparameters that define the HEN are passed to MP via the input filedenoted as “HEN” (see, e.g., FIG. 23) and the output is stored in thefile denoted as “RES.” As such, MP is defined over the file HEN and thestring OBJ, and program returns the file RES (i.e. RES←MP(HEN, OBJ)).

Sets:

S: Set of streams in the network, which includes hot and cold streams.N: Nodes in the network, including heat exchanger nodes, sources, andsinks. R: Source nodes (or terminal nodes), which are the startingpoints of a stream: R ∈ N RS: Set of pairs of streams and theircorresponding source nodes: R_(S) ∈ S × R. K: Sink nodes, which are theending point of a stream: K ∈ N. KS: Set of pairs of streams and theircorresponding sink (terminal) nodes: K_(S) F S × K. X: Heat exchangernodes, including process-to-process and utility exchangers. P:Process-to-process exchangers: P ∈ X. A process-to-process exchanger ismodeled by two nodes, one for the hot side and another for the coldside. PH: The hot nodes of the process-to-process exchangers used tomodel the hot side of the exchanger: P _(H) ∈ P. PC: The cold nodes ofthe process-to-process exchangers used to model the cold side of theexchanger: P_(C) ∈ P. L: Set of pairs of linked nodes to link the hotand cold sides of the process-to-process exchangers: L ∈ P _(H) × P_(C).U: The utility nodes, which include hot utilities and cold utilities: U∈ X. UH: The hot utility nodes used to heat cold streams: U _(H) ∈ U.UC: The cold utility nodes used to cool hot streams: U_(C) ∈ U. B: Theset of triples to represent branches in the HEN cold nodes of theprocess-to- process exchangers, used to model the cold side of theexchanger: B ∈ S × N × N. The first entry represents the stream, thesecond represents the starting node of the branch, and the thirdrepresents the terminal node of the branch.

Parameters:

-   -   Streams:

t_(s) ^(min)[t ∈ S]: The lower limit of a stream's starting temperature.t_(s) ^(max)[t ∈ S]: The upper limit of a stream's starting temperature.t_(t) ^(min)[t ∈ S]: The lower limit of a stream's target temperature.t_(t) ^(max)[t ∈ S]: The upper limit of a stream's target temperature.cp_(S) ^(min)[t ∈ S]: The lower limit of a stream's specific heat.cp_(S) ^(max)[t ∈ S]: The upper limit of a stream's specific heat. f_(S)^(min)[t ∈ S]: The lower limit of a stream's mass flow. f_(S) ^(max)[t ∈S]: The upper limit of a stream's mass flow.

-   -   Process-to-process exchangers:

Δt_(min) ^(P)[(i, j) ∈ L]: The minimum approach temperature differenceof a process-to-process heat exchanger. u_(p) ^(min)[(i, j) ∈ L]: Thelower limit of the overall heat transfer coefficient of aprocess-to-process heat exchanger. u_(P) ^(max)[(i, j) ∈ L]: The upperlimit of the overall heat transfer coefficient of a process-to-processheat exchanger.

-   -   Utility exchangers:

t_(U) ^(min)[i ∈ U]: The lower limit of a utility's temperature. t_(U)^(max)[i ∈ U]: The upper limit of a utility's temperature. Δt_(min)^(U)[i ∈ U]: The minimum approach temperature difference of a utilityheat exchanger. u_(U) ^(min)[i ∈ U]: The lower limit of the overall heattransfer coefficient of a utility heat exchanger. u_(U) ^(max)[i ∈ U]:The upper limit of the overall heat transfer coefficient of a utilityheat exchanger. q_(U) ^(min)[i ∈ U]: The lower limit of the overall heatduty transferred through a utility exchanger. q_(U) ^(max)[i ∈ U]: Theupper limit of the overall heat duty transferred through a utilityexchanger.

Variables:

-   -   Streams:

t_(s)[i ∈ s]: Stream's starting temperature. t_(t)[i ∈ S]: Stream'starget temperature. cp_(S)[i ∈ S]: Stream's specific heat. f_(S)[i ∈ S]:Stream's mass flow.

-   -   Branches:

f[(i, j, k) ∈ B]: Branch's mass flow rate. cp[( i, j, k) ∈ B]: Branch'sspecific heat. fcp[(i, j, k) ∈ B]: Branch's heat capacity flow rate.t[(i, j, k) ∈ B]: Temperature of fluid in a branch of the network.

-   -   Heat exchangers:

f_(x)[i ∈ X]: Total mass flow into/out of an exchanger. fcp_(x)[i ∈ x]:Total heat capacity flow rate through one side of an exchanger. t_(in)[i∈ X]: Temperature of fluid entering an exchanger. t_(out)[i ∈ X]:Temperature of fluid leaving an exchanger.

-   -   Process-to-process exchangers:

Δt_(p) ¹[(i, j) ∈ L]: The temperature difference between the enteringhot fluid and the leaving cold fluid in a process-to- process exchanger.Δt_(p) ²[(i, j) ∈ L]: The temperature difference between the leaving hotfluid and the entering cold fluid in a process-to- process exchanger.u_(p)[(i, j) ∈ L]: The overall heat transfer coefficient of a process-to-process heat exchanger. Δt_(LMTD) ^(P)[(i, j) ∈ L]: The log meantemperature difference of a process- to-process exchanger. q_(P)[(i, j)∈ L]: The overall heat duty transfer through a process- to-processexchanger. α_(P)[(i, j) ∈ L]: The surface area of a process-to-processheat exchanger.

-   -   Utility exchangers:

t_(U)[i ∈ U]: Utility's temperature. Δt_(U) ¹[i ∈ U]: The temperaturedifference between the entering hot fluid and the leaving cold fluid ina utility exchanger. Δt_(U) ²[i ∈ U]: The temperature difference betweenthe leaving hot fluid and the entering cold fluid in a utilityexchanger. Δt_(LMTD) ^(U)[(i, j) ∈ L]: The log mean temperaturedifference of a utility exchanger. u_(U)[i ∈ U]: The overall heattransfer coefficient of a utility heat exchanger. q_(U)[i ∈ U]: Theoverall heat duty transfer through a utility exchanger. α_(U)[i ∈ U]:The surface area of a utility heat exchanger.

Constraints:

-   -   Streams:

Stream temperature, specific heat, and flow limits are as follows:

t

^(min)[t]≦t

[t]≦t

^(max)[t] ∀ t ε S,

t_(t) ^(min)[t]≦t_(t)[t]≦t_(t) ^(max)[t] ∀ t ε S,

cp

^(min)[t]≦cp

[t]≦cp

^(max)[t] ∀ t ε S,

f

^(min)[t]≦f

[t]≦f

^(max)[t] ∀ t ε S.

Total material flow in the branches out of a source of a stream isequivalent to the stream's mass flow, as follows:

${f_{s}\lbrack i\rbrack} = {\sum\limits_{{({i,j,k})}{{\varepsilon B}:{{({i,j})}{\varepsilon R}_{S}}}}{{f\left\lbrack {i,j,k} \right\rbrack}{\forall{i \in {S.}}}}}$

Note, this constraint need not be specified for the sink because thematerial balance of the network guarantees this condition.

The temperatures of fluid in branches leaving a source of a stream areequivalent to the stream's temperature, as follows:

t[

,j,k]=t

[t] ∀(t,j,k)ε B:(t,j)ε R

.

The temperature resulting from the mix of fluids in branches going intoa sink equals the sink's stream's target temperature, as follows:

${{t_{t}\lbrack i\rbrack} \cdot {f_{S}\lbrack i\rbrack}} = {\sum\limits_{{({i,j,k})}{{\varepsilon B}:{{({i,k})}{\varepsilon K}_{S}}}}{{{t\left\lbrack {i,j,k} \right\rbrack} \cdot {f\left\lbrack {i,j,k} \right\rbrack}}\mspace{14mu} {\forall{i \in {S.}}}}}$

-   -   Branches:

Specific heat of branches equals that of their corresponding streams asfollows:

cp[t

j

k]=cp

[t] ∀(t

j

k,)ε B.

Heat capacity flow rate of branches equals the product of their massflow rate and their specific heat as follows:

fcp[t

j

k]=f[t

j

k]·cp[t

j

k] ∀(t,j,k)C B.

-   -   All heat exchangers:

The temperature resulting from the mix of fluids in branches going intoa heat exchanger equals the exchanger's entering temperature as follows:

${{t_{in}\lbrack k\rbrack} \cdot {f_{x}\lbrack k\rbrack}} = {\sum\limits_{{({i,j,k})} \in B}{{{t\left\lbrack {i,j,k} \right\rbrack} \cdot f}\left\lceil {i,j,k} \right\rceil \mspace{14mu} {\forall{k \in {X.}}}}}$

The temperatures of fluid in branches leaving a heat exchanger areequivalent to the exchanger's leaving temperature as follows:

t[t_(r)j_(r)k]=t_(out)[

]]∀(t_(r)j_(r)k,) ε B:j ε X.

Material balance: The heat capacity flow rate through an exchanger isequivalent to the total heat capacity flow rates of the enteringbranches, and the total heat capacity flow rates of the leavingbranches, as follows:

${{{fcp}_{x}\lbrack k\rbrack} = {\sum\limits_{{({i,j,k})} \in B}{{{fcp}\left\lbrack {i,j,k} \right\rbrack}\mspace{14mu} {\forall{k:{\left( {i,j,k} \right) \in B}}}}}},{{{fcp}_{x}\lbrack j\rbrack} = {\sum\limits_{{({i,j,k})} \in B}{{{fcp}\left\lbrack {i,j,k} \right\rbrack}\mspace{14mu} {\forall{j \in {X:{\left( {i,j,k} \right) \in {B.}}}}}}}}$

-   -   Process-to-process exchangers:

Calculation of the two approach temperatures of an exchanger, where thefirst is the difference between the entering hot stream's temperatureand the leaving cold stream's temperature, and the second is thedifference between the leaving hot stream's temperature and the enteringcold stream's temperature, is as follows:

Δt_(p) ¹[t

j]=t_(in)[t]−t_(out)[j] ∀(t,j)ε L,

Δt_(p) ²[t

j]=t_(out)[t]−t_(in)[j] ∀(t,j)ε L.

The two approach temperatures are no less than the minimum approachtemperature of the exchanger, as follows:

Δt

¹[t,j]≧Δt_(min)

[t,j] ∀(t,j)ε L,

Δt

²[t,j]≧Δt_(min)

[t,j] ∀(t,j)ε L.

Heat transferred in an exchanger equals the heat lost from the hot sideof the exchanger, as follows:

[t

j]=(t_(in)[t] t_(out)[t])·fcp_(X)[t] ∀(t

j)C L.

Heat transferred in an exchanger equals the heat gained in the cold sideof the exchanger, as follows:

[t

j]=(t_(out)[j]−t_(in)[j]−t_(in)[j])·fcp_(X)[j]]∀(t,j)ε L.

The calculation of the log mean temperature difference of aprocess-to-process heat exchanger should be as follows for enhancedaccuracy:

${\Delta \; {t_{LMTD}^{P}\left\lbrack \left( {i,j} \right) \right\rbrack}} = {\frac{{\Delta \; {t_{P}^{1}\left\lbrack {i,j} \right\rbrack}} - {\Delta \; {t_{P}^{2}\left\lbrack {i,j} \right\rbrack}}}{\ln \left( \frac{\Delta \; {t_{P}^{1}\left\lbrack {i,j} \right\rbrack}}{{\Delta \;}_{P}^{2}\left\lbrack {i,j} \right\rbrack} \right)}\mspace{14mu} {\forall{\left( {i,j} \right) \in {L.}}}}$

Due to the computational expense of solving problems with thelogarithmic function, however, according to the exemplary configuration,the calculation is performed utilizing the Chen's approximation, whichis:

${\Delta \; {t_{LMTD}^{P}\left\lbrack \left( {i,j} \right) \right\rbrack}} = {\Delta \; {{t_{P}^{1}\left\lbrack {i,j} \right\rbrack} \cdot \Delta}\; {{t_{P}^{2}\left\lbrack {i,j} \right\rbrack} \cdot \sqrt[2]{\frac{{\Delta \; {t_{P}^{1}\left\lbrack {i,j} \right\rbrack}} + {\Delta \; {t_{P}^{2}\left\lbrack {i,j} \right\rbrack}}}{2}}}\mspace{14mu} {\forall{\left( {i,j} \right) \in {L.}}}}$

Heat transfer of process-to-process exchangers as a function of heatexchanger area, is as follows:

[t,j]=α

[t

j]·α

[t

j]·Δt_(LVED)

[t

j)] ∀(t

j)ε L

The overall heat transfer coefficient limits are as follows:

u

^(min)[t

j)≦u

[t

j]≦u

^(max)[t

j] ∀(t

j)ε L.

All Utility Heat Exchangers:

Chen's approximation of the log mean temperature difference for utilityexchangers is as follows:

${\Delta \; {t_{LMTD}^{U}\lbrack i\rbrack}} = {\Delta \; {{t_{U}^{1}\lbrack i\rbrack} \cdot \Delta}\; {{t_{U}^{2}\lbrack i\rbrack} \cdot \sqrt[2]{\frac{{\Delta \; {t_{U}^{1}\lbrack i\rbrack}} + {\Delta \; {t_{U}^{2}\lbrack i\rbrack}}}{2}}}\mspace{14mu} {\forall{t \in {U.}}}}$

Limits for the overall heat transfer coefficient, the overall heat dutytransfer, and the utilities temperature, are as follows:

u_(U)

[i]≦u_(U)[i]≦u_(U) ^(max)[i] ∀]i ε U,

_(U)

[t]≦

_(U)[i]≦

_(U) ^(max)[i] ∀ t ε U,

t_(U)

[i]≦

_(U)[i]≦

_(U) ^(max)[i] ∀ t ε U.

The two approach temperatures are no less than the minimum approachtemperature of the exchanger, as follows:

Δt

²[t]≧Δt

^(U)[t] ∀ t ε U.

Heat transfer of utility exchangers as a function of heat exchangerarea, is as follows:

α_(U)[t]=u_(U)[t]·α_(U)[t]·Δt

^(U)[t] ∀ t ε U.

-   -   Hot utility exchanger:

of the two approach temperatures of a utility exchanger, where the firstis the difference between the utility's temperature and the leavingprocess stream's temperature, and the second is the difference betweenthe utility's temperature and the entering process stream's temperature,is as follows:

Δt_(U) ¹[t]−t_(U)[t]−t_(out)[i] ∀ t ε U_(E),

Δt_(U) ²[t,j]=t_(U)[t]−t_(in)[j] ∀ t ε U_(H).

The smaller approach temperature (utility's temperature minus outletprocess temperature) is no less than the minimum approach temperature ofthe exchanger, as follows:

Δt_(U) ¹[t]–Δt_(min) ^(U)[t] ∀ t ε U_(H).

Heat transferred in an exchanger equals the heat gained by the processstream, as follows:

_(U)[t]=(t_(out)[t]−t

[t])·fcp_(X)[t] ∀ t ε U_(H).

-   -   Cold utility exchanger:

Calculation of the two approach temperatures of a utility exchanger,where the first is the difference between the entering process stream'stemperature and the utility's temperature, and the second is thedifference between the leaving process stream's temperature and theutility' temperature, or as follows:

Δ_(U) ¹[t]=t

[t]−t_(U)[t] ∀ t ε U_(C),

Δt_(U) ²[t

j]=t_(out)[t]−t_(U)[j] ∀ t ε U_(C).

The smaller approach temperature (outlet process temperature minus theutility's temperature) is no less than the minimum approach temperatureof the exchanger, as follows:

Δt

[t]≧Δt_(min) ^(U)[t] ∀ t ε U_(C).

Heat transferred in an exchanger equals the heat lost in the processstream, as follows:

_(U)[t]=(t_(in)[t]−t_(out)[t])·fcp_(X)[t] ∀ t ε U_(C).

According to exemplary embodiment of the present invention, themathematical program can automatically calculate the minimum (justneeded) and maximum surface area for each heat exchanger unit and thecorresponding the minimum and maximum total surface area for the wholenetwork that satisfies the user input/given process conditionsvariations (disturbances/uncertainties) schemes. The mathematicalprogram can also determine, from the user input/givenintervals/operating windows/ranges describing the values for the processstreams supply and target temperatures as well as streams heat capacityflow rates, the optimal set of process conditions that render theminimum total surface area of heat exchangers network and the optimalset of process conditions that render the maximum total surface area ofthe designed heat exchangers network. In an alternative embodiment ofthe mathematical program, the program can further and/or alternativelydetermine the set of process conditions that render the optimal requiredsurface area of the heat exchangers network.

It is important to note that while the foregoing embodiments of thepresent invention have been described in the context of a fullyfunctional system and process, those skilled in the art will appreciatethat the mechanism of at least portions of the present invention and/oraspects thereof are capable of being distributed in the form of anon-transitory tangible computer readable medium in a variety of formsstoring a set of instructions for execution on a processor, processors,or the like, where it is understood that non-transitorycomputer-readable media comprises all tangible computer-readable media,with the sole exception being a transitory, propagating signal, and thatembodiments of the present invention apply equally regardless of theparticular type of signal bearing media used to actually carry out thedistribution. Examples of the computer readable media include, but arenot limited to: nonvolatile, hard-coded type media such as read onlymemories (ROMs), CD-ROMs, and DVD-ROMs, or erasable, electricallyprogrammable read only memories (EEPROMs), recordable type media such asfloppy disks, hard disk drives, CD-R/RWs, DVD-RAMs, DVD-R/RWs,DVD+R/RWs, HD-DVDs, memory sticks, mini disks, laser disks, Blu-raydisks, flash drives, and other newer types of memories, and certaintypes of transmission type media such as, for example, certain digitaland analog communication links that are capable of storing the set ofinstructions. Such media can contain, for example, both operatinginstructions and the operations instructions related to the programproduct 51 and the computer executable portions of the algorithms andmethod steps according to various embodiments of a method ofsynthesizing a grass-roots heat exchanger network for a plurality of hotprocess streams to be cooled and a plurality of cold process streams tobe heated and to identify optimal heat exchanger network topology, andvarious embodiments of a method to synthesize a grass-roots heatexchanger network for a plurality of hot process streams to be cooledand a plurality of cold process streams to be heated and to identifyoptimal heat exchanger network topology for future retrofit toaccommodate future time-dependent new operating modes, disturbances anduncertainty schemes.

Embodiments of the present invention provide numerous advantages andbenefits. For example, various exemplary embodiments of the presentinvention introduce a systematic user friendly system, method, andprogram product for grassroots heat exchangers network synthesis thatexhibits life-Cycle switchability and flexibility under all anticipatedpossible combinations of process variations with procedures forretrofitability due to change in energy and capital cost trade-offand/or change in assumed design phase disturbance and/or uncertaintyschemes. Exemplary embodiments of the present invention advantageouslykeep the designer in control for the synthesis of the network, andadvantageously do not require the use of assumptions that confine thesynthesized network to inferior structures due to the use of unrealisticassumptions regarding disturbance and uncertainty schemes. Nor doexemplary embodiments of the present invention require use of asimplified multi-period superstructure for the network to avoid itscombinatorial explosion (i.e., due to a requirement for sets of theP-dimensional vectors) as is the situation in the mathematicalprogramming-based methods which utilize sets of multi-dimensionalvectors. In contrast, various exemplary embodiments of the presentinvention can readily dispatch industrial-size problems, can allow thedesigner to test his/her novel solutions for network synthesis, canemploy a realistic disturbance and uncertainty scheme, can utilize abest estimate for operating cost calculation to thereby result in thesynthesis of networks that exhibits a minimum number of units with aminimum value for the maximum required surface area, done systematicallyand without manual iteration (required when employing a conventionalpinch-based approach).

Exemplary embodiments of the present invention can furtheradvantageously produce, systematically, networks having life-cycleswitchability and flexibility as well as easiness in heat exchangersnetwork future systematic retrofitability. Additionally, exemplaryembodiments of the present invention can determine optimal targettemperatures at the design phase under all anticipated possiblecombinations of disturbances and uncertainty for streams with operatingwindow range. Further, besides deciding the optimal target temperaturefrom heat exchanger network capital and operating cost costs, variousexemplary embodiments of the invention can use the target temperaturerange of each stream in a performance equation of the rest of theprocess to ascertain its economic impact on the rest of the process. Insuch case the streams optimal target temperatures can be optimallyselected for each stream based upon its impact on process economics,energy consumption, and switchable and flexible heat exchanger networkcapital cost. Accordingly, such systematic methods/techniques, systems,and program product can substantially benefit the heat exchangersnetwork synthesis and waste heat recovery applications of new plantdesigns and its future retrofit in a world of fast dynamics withsignificant changes in energy availability and prices.

Various exemplary embodiments of the present invention furtheradvantageously introduce a systematic heat exchangers network synthesisprocess/technique that renders desirable improvements over the pinchapproach. For example, where the pinch approach is an in-systematic adhoc iterative approach, which, in the case of the nominal design, is notunderstood to provide solutions which include matching one or more hotstreams with one or more hot streams or one or more cold streams withone or more cold streams, and/or partially converting one or more hotstreams to one or more cold streams or one or more cold streams to oneor more hot streams, various embodiments of the present invention canprovide such solutions. Further, as is the case of nominal design, wherethe pinch approach is not understood to provide any guarantee offeasibility under a given realistic disturbance scheme—instead producinga heat exchangers network with a greater than optimal number of units;does not address life cycle switchability and flexibility; and can notbe used to calculate optimal target temperatures for streams within arealistic operating window range at the design phase under all possiblecombinations of anticipated disturbances and uncertainty, variousembodiments of the present invention advantageously provide suchsolutions.

Various exemplary embodiments of the present invention can utilizevarious input values to synthesize, systematically, a switchable heatexchangers network with a desired level of flexibility under allpossible anticipated combinations of process variations for a process orcluster of processes using a plurality of resource streams havingoperational attributes, which exhibits various desirable qualitiesaccording to various specific procedures. Such synthesized networkdeveloped therefrom can advantageously include one that exhibitseasiness for life-cycle switchability and flexibility retrofitabilitysynthesized according to specific procedures: that achieve at least oneobjective which exactly satisfies certain heating and cooling utilitiesloads, that achieve at least one objective using a fewer number ofunits, that achieve at least one objective satisfying more or less, inbounded range, certain heating and cooling utilities, that achieve atleast one objective comprising either a heating or cooling utility, thatachieve at least one objective comprising less hot utility consumption,that achieve at least one objective comprising less cold utilityconsumption, that achieve at least one objective comprising a lessernumber of hot utilities types, that achieve at least one objectivecomprising a lesser number of cold utilities types, that achieve atleast one objective comprising less degradation in process sourceregion, and/or that achieve at least one objective comprising theachievement of a minimum value for the maximum surface area required toachieve the network objectives under all possible combinations of givenprocess variations.

Such synthesized network developed therefrom can also or alternativelyadvantageously include one that exhibits easiness for life-cycleswitchability and flexibility retrofitability synthesized according tospecific procedures: that achieve at least the two objectives comprisingless degradation in the process source region and exact intervalconsumption of heating and cooling utilities, that achieve at least thetwo objectives comprising less degradation in the process source regionand a minimum maximum surface area required to satisfy all possiblecombinations for the given range of process variations, that achieve atleast the two objectives comprising using a fewer number of units and aminimum maximum surface area that is required to handle all possiblecombinations of the given interval range of process variations, and/orthat achieve at least three objectives comprising satisfying intervalenergy consumption exactly using a fewer number of units and a minimummaximum surface area that is required to handle all possiblecombinations of a given interval range of process variations.

Such synthesized network developed therefrom can advantageously also oralternatively include one that exhibits easiness for life-cycleswitchability and flexibility retrofitability synthesized according tospecific procedures that provide an indication of the specific attributevalue or values determined from the ranges supplied by the user in thebeginning or even decided during the implementation of the proceduresfor the streams target temperatures which result in a new utilityconsumption value or values calculated and the heat exchanger networksynthesized to achieve one or more of the accompanied objectivesdescribed above. This can include synthesizing a systematicallyswitchable heat exchanger network with a desired level of flexibilitythat exhibits easiness for life-cycle switchability and flexibilityretrofitability with optimally selected streams target temperatures,whereby the calculated utilities consumption value or values satisfydesired minimum utilities consumed to heat resource streams and minimumutilities consumed to cool resource streams, while considering certainprocess constraints. Such synthesized network developed therefrom canadvantageously also or alternatively include one that exhibits easinessfor life-cycle switchability and flexibility retrofitability synthesizedaccording to specific procedures: that include performing an automatedcalculation of [Q], [A], [Fcp], and middle temperatures in the networkfor the desired heat exchanger network structure, that rigorouslyprovide sharp bounds on surface area calculations, that calculateconditions that result in the worst case scenarios for single heatexchangers as well as for the total network surface area under allpossible combinations of process variations, and/or that determinemaximum flow limits in the branches of the network that result from allthe possible combinations process variations, which can be used todetermine the branch capacities before the detailed design isaccomplished.

This application is related to U.S. Provisional Patent Application No.61/356,900, filed Jun. 21, 2010, titled “Systematic Synthesis Method andProgram Product For Heat Exchanger Network Life-Cycle Switchability andFlexibility Under All Possible Combinations of Process Variations,” U.S.Provisional Patent Application No. 61/256,754, filed Oct. 30, 2009,titled “System, Method, and Program Product for SynthesizingNon-Constrained and Constrained Heat Exchanger Networks and IdentifyingOptimal Topology for Future Retrofit, U.S. patent application Ser. No.12/575,743, filed Oct. 8, 2009, titled “System, Method, and ProgramProduct for Targeting and Identification of Optimal Process Variables inConstrained Energy Recovery Systems, U.S. patent application Ser. No.12/715,255, filed Mar. 1, 2010, titled “System, Method, and ProgramProduct for Targeting and Optimal Driving Force Distribution in EnergyRecovery Systems,” U.S. patent application Ser. No. 11/768,084, filed onJun. 25, 2007, titled “System, Method, and Program Product for Targetingand Optimal Driving Force Distribution in Energy Recovery Systems,” U.S.Provisional Patent Application No. 60/816,234, filed Jun. 23, 2006,titled “Method and Program Product for Targeting and Optimal DrivingForce Distribution in Energy Recovery Systems,” U.S. patent applicationSer. No. 12/480,415, filed Jun. 8, 2009, titled “System, Program Productand Related Methods for Global Targeting of Process Utilities UnderVarying Conditions,” U.S. patent application Ser. No. 12/767,217, filedApr. 26, 2010, titled “System, Method, and Program Product forSynthesizing Non-Constrained and Constrained Heat Exchanger Networks,”U.S. patent application Ser. No. 12/767,275, filed Apr. 26, 2010, titled“System, Method, and Program Product for SynthesizingNon-Thermodynamically Constrained Heat Exchanger Networks,” and U.S.patent application Ser. No. 12/767,315, filed Apr. 26, 2010, titled“System, Method, and Program Product for Synthesizing Heat ExchangerNetworks and Identifying Optimal Topology for Future Retrofit,” eachincorporated herein by reference in its entirety.

In the drawings and specification, there have been disclosed a typicalpreferred embodiment of the invention, and although specific terms areemployed, the terms are used in a descriptive sense only and not forpurposes of limitation. The invention has been described in considerabledetail with specific reference to these illustrated embodiments. Thisinvention is not to be construed as limited to the particular forms orembodiments disclosed, since these are regarded as illustrative ratherthan restrictive. It will be apparent, however, that variousmodifications and changes can be made within the spirit and scope of theinvention as described in the foregoing specification.

1. A method to synthesize a grass-roots heat exchanger network for aprocess or cluster of processes having a plurality of hot processstreams to be cooled and a plurality of cold process streams to beheated and to identify optimal heat exchanger network topology, themethod comprising the steps of: synthesizing a plurality of heatexchanger network designs for a process comprising a plurality ofprocess streams, each of the plurality of heat exchanger network designssynthesized according to a corresponding different one of a plurality ofheat exchanger network process variations schemes, each heat exchangernetwork exchanger network process variations scheme including a set ofprocess stream supply attribute values each separately associated with adifferent one of the plurality of process streams and having a level ofsupply attribute value feasibility being different from the level ofsupply attribute value feasibility for each other of the plurality ofheat exchanger network process variations schemes; determining capitaland operating costs associated with employing a first heat exchangernetwork process variations scheme on a first heat exchanger networkdesign of the plurality of heat exchanger network designs; determiningcapital and operating costs associated with employing a second heatexchanger network process variations scheme on a second heat exchangernetwork design of the plurality of heat exchanger network designs;applying a supply attribute value range of variation of one of theprocess streams of the plurality of process streams according to thesecond heat exchanger network process variations scheme defining asecond supply attribute value range of variation to the supply attributefor the one of the process streams for the first heat exchanger networkdesign defining a first supply attribute value range of variation tothereby identify a cost impact of an associated change in targettemperature thereof resulting from application of the second supplyattribute value range of variation thereto; and determining aprocess-cost-impact of a deviation in target temperature range ofvariation for one or more of the process streams for the first heatexchanger network design responsive to application of the second supplyattribute value range of variation to the supply attribute of the one ofthe process streams for the first heat exchanger network design tothereby determine when the first heat exchanger network design providesa more optimal heat exchanger network design than the second heatexchanger network design and when the first heat exchanger networkprocess variations scheme correspondingly represents a more optimalflexibility index.
 2. A method as defined in claim 1, further comprisingthe steps of: determining a target temperature range value for the oneof the process streams of the plurality of process streams defining anexpected sub-optimal target temperature range value responsive to thestep of applying the second supply attribute value range of variation tothe supply attribute of the one of the process streams for the firstheat exchanger network design; determining a target temperature rangevalue for each other of the plurality of process streams responsive tothe step of applying the second supply attribute value range ofvariation to the supply attribute of the one of the process streams forthe first heat exchanger network design; the process-cost-impactcomprising an impact of the expected sub-optimal target temperaturerange value for the one of the process streams and any changes in thetarget temperature range value for each other of the plurality ofprocess streams on total process economics resulting from application ofthe second supply attribute value range of variation on the first heatexchanger network design; and determining the first heat exchangernetwork design according to the first heat exchanger process variationsscheme to be the optimal heat exchanger network design and the firstheat exchanger network process variations scheme to represent theoptimal system-level flexibility index when the difference in capitalcost and operating cost between the first and the second heat exchangernetwork designs is higher than the process-cost-impact.
 3. A method asdefined in claim 1, wherein the one of the process streams of theplurality of process streams is a first one of a plurality of processstreams being evaluated, wherein the supply attribute comprises supplytemperature, wherein the first supply attribute value range of variationcomprises a first supply temperature range of variation, wherein thesecond supply attribute value range of variation comprises a secondsupply temperature range of variation, and wherein the step ofdetermining a process-cost-impact further comprises the steps of:determining an economic impact of a deviation in target temperaturerange of variation for each other of the plurality of process streamsfor the first heat exchanger network design when existing responsive toapplication of the second supply temperature range of variation of therespective process stream under evaluation according to the second heatexchanger network process variations scheme to the supply temperature ofthe respective process stream under evaluation for the first heatexchanger network design, to include performing the following steps foreach other of the plurality of process streams: applying the secondsupply temperature range of variation of the respective process streamunder evaluation according to the second heat exchanger network processvariations scheme, to the supply temperature of the respective processstream under evaluation for the first heat exchanger network design,determining a target temperature range value for the respective processstream under evaluation defining an expected sub-optimal targettemperature range value for the respective process stream underevaluation responsive to the step of applying the second supplytemperature range of variation of the respective process stream underevaluation according to the second heat exchanger network processvariations scheme to the supply temperature of the respective processstream under evaluation for the first heat exchanger network design tothereby determine an economic impact of the expected sub-optimal targettemperature range value for the one of the process streams on totalprocess economics, determining a target temperature range value for eachother of the plurality of process streams of the process responsive tothe step of applying the second supply temperature range of variation ofthe respective process stream under evaluation according to the secondheat exchanger network process variations scheme to the supplytemperature of the respective process stream under evaluation for thefirst heat exchanger network design to thereby determine an economicimpact of changes in the target temperature range value for each otherof the plurality of process streams on total process economics as aresult of application of the second supply temperature range ofvariation on the first exchanger network design, and determining thetotal economic cost resulting from application of the respective secondsupply temperature range of variation of the respective process streamunder evaluation according to the second heat exchanger network processvariations scheme to the supply temperature of the respective processstream under evaluation for the first heat exchanger network designresponsive to determining an economic impact of the expected sub-optimaltarget temperature range value for the respective process stream underevaluation and responsive to determining an economic impact of changesin the target temperature range value for each other of a plurality ofprocess streams; and identifying each target temperature range ofvariation of the first heat exchanger network process variations schemehaving a substantial economic impact on the process as a whole.
 4. Amethod as defined in claim 3, further comprising performing at least oneof the following steps: determining stream-specific target temperatureflexibility level priority by economic impact on the process as a wholedefining a stream-specific-flexibility-level prioritization schemebetween each of the plurality of process streams responsive toapplication of a plurality of different supply temperature ranges ofvariation to each of a plurality of process streams under evaluation;and assigning a stream-specific target temperature flexibility prioritylevel to each target temperature range of variation of each of theplurality of process streams having a substantial economic impact on theprocess as a whole.
 5. A method as defined in claim 1, furthercomprising the step of: determining a stream-specific flexibilitypriority list for the plurality of process streams, the stream-specificflexibility priority list including a separate stream-specificflexibility level associated with each separate one of the plurality ofprocess streams, at least two of the stream-specific flexibility levelsbeing different from each other.
 6. A method as defined in claim 1,further comprising the step of: determining a stream-specific targettemperature flexibility priority list for the plurality of processstreams, the stream-specific target temperature flexibility prioritylist including a plurality of different stream-specific targettemperature flexibility levels for each separate one of one or more ofthe plurality of process streams.
 7. A method as defined in claim 1,further comprising the step of: determining a supply attributecriticality list of process stream supply attribute ranges of variationsfor the plurality of process streams, the criticality list including aseparate range of variations for each of the plurality of processstreams wherein a deviation in the range of variation thereto results ina substantial economic impact on the process as a whole.
 8. A method asdefined in claim 7, wherein the process stream supply attribute rangesof variations include supply temperature ranges of variations for thesupply temperatures for each of the plurality of process streams, themethod further comprising the step of: determining a supply attributecriticality list of heat capacity flow rates range of variations foreach of the plurality of process streams wherein a deviation in the heatcapacity flow rate range of variation thereto results in a substantialeconomic impact on the process as a whole.
 9. A method as defined inclaim 1, further comprising the step of: determining a supply attributecriticality list of process stream supply attribute ranges of variationsfor the plurality of process streams, the criticality list including aplurality of different ranges of variations for each separate one of oneor more of the plurality of process streams.
 10. A method as defined inclaim 1, further comprising for each of the plurality of heat exchangernetwork designs associated with the corresponding plurality of the heatexchanger network process variations schemes, the step of analyzing atriple trade-off between estimated energy operating cost of therespective heat exchanger network design, estimated heat exchangernetwork capital costs, and estimated process-cost-impact at each of aplurality of individual process stream flexibility levels.
 11. A methodas defined in claim 1, wherein the set of process stream supplyattribute values includes a set of a plurality of supply temperatureshaving a level of supply temperature feasibility being different fromthe level of supply temperature feasibility for each other of theplurality of heat exchanger network process variations schemes; whereinthe first supply attribute value range of variation comprises a firstsupply temperature range of variation; wherein the second supplyattribute value range of variation comprises a second supply temperaturerange of variation; wherein the step of synthesizing a plurality of heatexchanger network designs for a process comprises the steps of:synthesizing the first heat exchanger network design for the processaccording to the first heat exchanger network process variations scheme,the one of the process streams of the plurality of process streams forthe first heat exchanger network design including a design supplytemperature having the first supply temperature range of variationdefining a first level of flexibility according to a first probabilityand having a corresponding first design target temperature range ofvariation, and synthesizing the second heat exchanger network design forthe process according to the second heat exchanger network processvariations scheme, the one of the process streams for the second heatexchanger network design including a design supply temperature havingthe second supply temperature range of variation defining a second levelof flexibility according to a second probability and having acorresponding second target temperature range of variation, the secondsupply temperature range of variation of the one of the process streamsof the plurality process streams according to the second heat exchangernetwork variations scheme providing a higher level of flexibility thanthe first supply temperature range of variation of the one of theplurality of process streams according to the first heat exchangernetwork variations scheme and having a higher implementation cost;wherein the step of applying a supply attribute value range of variationof one of the process streams of the plurality of process streamsaccording to the second heat exchanger network process variations schemeto the supply attribute for the one of the process streams for the firstheat exchanger network design comprises the step of: assigning thesecond supply temperature range of variation of the one of the processstreams to the supply temperature of the one of the process streams forthe first heat exchanger network design with the supply temperaturevalues for each other of the plurality of process streams according tothe first heat exchanger network process variations scheme remainingunchanged, the design second supply temperature range of variationhaving a narrower range of values than that of the design first supplytemperature range of variation of the supply temperature of the one ofthe process streams for the first heat exchanger network design, thedesign second target temperature range of variation having a wider rangeof values than that of the design first target temperature range ofvariation of the target temperature of the one of the process streamsfor the first heat exchanger network design.
 12. A method as defined inclaim 11, wherein the second heat exchanger network process variationsscheme provides a higher level of flexibility than each other of theplurality of heat exchanger network process variations schemes; whereineach other of the plurality of heat exchanger network process variationsschemes have successively lower levels of flexibility than that of thesecond heat exchanger network process variations scheme; and wherein themethod further comprises the step of determining an economic impact of achange in target temperature of one or more associated process streamsfor each other of the plurality of heat exchanger network designsdefining a plurality of heat exchanger network designs under evaluationresulting from application of the second supply temperature range ofvariation of the supply temperature of the respective one or moreprocess stream to the supply temperature of the respective one or moreprocess streams of the respective heat exchanger network design underevaluation, to include performing the following steps for each of theplurality of heat exchanger network designs under evaluation:determining capital and operating costs associated with the heatexchanger network design under evaluation employing the design specifiedheat exchanger network process variations scheme, applying the secondsupply temperature range of variation of the one or more process streamsaccording to the second heat exchanger network process variations schemeto the supply temperature of the one or more process streams for, theheat exchanger network design under evaluation, determining the targettemperature range value for the one or more process streams defining anexpected sub-optimal target temperature range value for the respectiveprocess stream responsive to the step of applying the second supplytemperature range of variation of the one or more process streamsaccording to the second heat exchanger network process variations schemeto the supply temperature of the one or more process streams for theheat exchanger network design under evaluation to thereby determine aneconomic impact of the expected sub-optimal target temperature rangevalue for the one or more process streams on total process economics,determining the target temperature range value for each other of theplurality of process streams responsive to the step of applying thesecond supply temperature range of variation of the one or more processstreams according to the second heat exchanger network processvariations scheme to the supply temperature of the one or more processstreams for the heat exchanger network design under evaluation tothereby determine an economic impact of changes in the targettemperature range value for each other of the plurality of processstreams on total process economics, and determining theprocess-cost-impact resulting from application of the second supplytemperature range of variation of the one or more process streamsaccording to the second heat exchanger network process variations schemeto the supply temperature of the one or more process streams for theheat exchanger network design under evaluation responsive to determiningan economic impact of the expected sub-optimal target temperature rangevalue for the respective one or more process streams and responsive todetermining an economic impact of changes in the target temperaturerange value for each other of a plurality of process streams to therebydetermine when the heat exchanger network design under evaluationprovides a more optimal heat exchanger network design than the secondheat exchanger network design and when the heat exchanger networkprocess variations scheme associated with the respective heat exchangernetwork design under evaluation correspondingly represents a moreoptimal flexibility index.
 13. A method as defined in claim 11, whereinthe second heat exchanger network process variations scheme provides ahigher level of flexibility than each other of the plurality of heatexchanger network process variations schemes; wherein each other of theplurality of heat exchanger network process variations schemes havesuccessively lower levels of flexibility than that of the second heatexchanger network process variations scheme; wherein the step ofsynthesizing a plurality of heat exchanger network designs furtherincludes identifying a third heat exchanger network process variationsscheme for a third heat exchanger network design synthesized for theprocess according to the third heat exchanger network process variationsscheme, the one of the process streams of the plurality of processstreams for the third heat exchanger network design including a designsupply temperature having a third supply temperature range of variationdefining a third level of flexibility according to a third probabilityand having a corresponding third target temperature range of variation,the third supply temperature range of variation of the one of theprocess streams according to the third heat exchanger network variationsscheme providing a lower level flexibility and higher implementationcost than both the first supply temperature range of variation of theone of the process streams according to the first heat exchanger networkvariations scheme and the second supply temperature range of variationof the one of the process streams according to the second heat exchangernetwork variations scheme; and wherein the method further comprises thesteps of: determining capital and operating costs associated withemploying the third heat exchanger network process variations scheme onthe third heat exchanger network design, applying the second supplytemperature range of variation of the one of the process streamsaccording to the second heat exchanger network process variations schemeto the supply temperature for the one of the process streams for thethird heat exchanger network design, with the supply temperature valuesfor each other of the plurality of process streams according to thethird heat exchanger network process variations scheme remainingunchanged, determining the target temperature range value for the one ofthe process streams defining an expected sub-optimal target temperaturerange value for the respective process stream responsive to the step ofapplying the second supply temperature range of variation of the one ofthe process streams according to the second heat exchanger networkprocess variations scheme to the supply temperature for the one of theprocess streams for the third heat exchanger network design to therebydetermine an economic impact of the expected sub-optimal targettemperature range value for the one of the process streams on totalprocess economics for the third heat exchanger network design,determining the target temperature range value for each other of theplurality of process streams responsive to the step of applying thesecond supply temperature range of variation of the one of the processstreams according to the second heat exchanger network processvariations scheme to the supply temperature for the one of the processstreams for the third heat exchanger network design to thereby determinean economic impact of changes in the target temperature range value foreach other of the plurality of process streams on total processeconomics, determining a process-cost-impact resulting from applicationof the second supply temperature range of variation of the one of theprocess streams according to the second heat exchanger network processvariations scheme to the supply temperature of the one of the processstreams for the third heat exchanger network process variations schemeresponsive to determining an economic impact of the expected sub-optimaltarget temperature range value for the respective one or more processstreams and responsive to determining an economic impact of changes inthe target temperature range value for each other of a plurality ofprocess streams to thereby determine when the third heat exchangernetwork design provides a more optimal heat exchanger network designthan both the first and the second heat exchanger network designs andwhen the third heat exchanger network process variations schemecorresponding represents the more optimal flexibility index, anddetermining the third heat exchanger process variations scheme to be theoptimal heat exchanger network process variations scheme and torepresent the optimal flexibility index when the difference in capitalcost and operating cost between the third and the second heat exchangerdesigns is higher than the process-cost-impact resulting fromapplication of the second supply temperature range of variation of atleast a subset of the plurality of process streams according to thesecond heat exchanger network process variations scheme to therespective supply temperatures of a corresponding at least a subset ofthe plurality of process streams for the third heat exchanger networkdesign.
 14. A method as defined in claim 11, wherein the step ofdetermining capital and operating costs associated with employing thefirst heat exchanger network process variations scheme on the first heatexchanger network design includes determining a cost of achieving thefirst target temperature range of variation for the one of the processstreams with the first probability; wherein the step of determiningcapital and operating costs associated with employing the second heatexchanger network process variations scheme on the second heat exchangernetwork design includes determining a cost of achieving the secondtarget temperature range of variation for the one of the process streamswith the second probability; wherein the method further comprises thestep of determining a difference in capital and operating costs betweenthe first and second heat exchanger network designs; wherein the firstprobability of achieving the first target temperature range of variationfor the one of the process streams according to the first heat exchangernetwork variations scheme is a certain discrete value that is less than100% when applied to the first exchanger network design; wherein thesecond probability of achieving the second target temperature range ofvariation for the one of the process streams according to the secondheat exchanger network variations scheme is approximately 100% whenapplied to the second heat exchanger network design; and wherein theprocess-cost-impact includes a cost impact of a deviation of the firsttarget temperature range value to a sub-optimal level for a certaindiscrete percentage of a time responsive to application of the secondsupply temperature range of variation of the supply temperature of theone of the process streams to the first heat exchanger network design.15. A method as defined in claim 1, wherein the set of process streamsupply attribute values includes a set of a plurality of heat capacityflow rates having a level of heat capacity flow rate feasibility beingdifferent from the level of heat capacity flow rate feasibility for eachother of the plurality of heat exchanger network process variationsschemes; wherein the first supply attribute value range of variationcomprises a first heat capacity flow rate range of variation; whereinthe second supply attribute value range of variation comprises a secondheat capacity flow rate range of variation; wherein the step ofsynthesizing a plurality of heat exchanger network designs for aprocess-comprises the steps of: synthesizing the first heat exchangernetwork design for the process according to the first heat exchangernetwork process variations scheme, the one of the process streams of theplurality of process streams for the first heat exchanger network designincluding a design heat capacity flow rate having the first heatcapacity flow rate range of variation defining a first level offlexibility according to a first probability and having a correspondingfirst design target temperature range of variation, and synthesizing thesecond heat exchanger network design for the process according to thesecond heat exchanger network process variations scheme, the one of theprocess streams for the second heat exchanger network design including adesign heat capacity flow rate having the second heat capacity flow raterange of variation defining a second level of flexibility according to asecond probability and having a corresponding second target temperaturerange of variation, the second heat capacity flow rate range ofvariation of the one of the process streams of the plurality processstreams according to the second heat exchanger network variations schemeproviding a higher level of flexibility than the first heat capacityflow rate range of variation of the one of the plurality of processstreams according to the first heat exchanger network variations schemeand having a higher implementation cost; wherein the step of applying asupply attribute value range of variation of the one of the processstreams of the plurality of process streams according to the second heatexchanger network process variations scheme to the supply attribute forthe one of the process streams for the first heat exchanger networkdesign comprises the step of: assigning the second heat capacity flowrate range of variation of the one of the process streams to the heatcapacity flow rate of the one of the process streams for the first heatexchanger network design with the heat capacity flow rate values foreach other of the plurality of process streams according to the firstheat exchanger network process variations scheme remaining unchanged,the design second heat capacity flow rate range of variation having anarrower range of values than that of the design first heat capacityflow rate range of variation of the heat capacity flow rate of the oneof the process streams for the first heat exchanger network design, thedesign second target temperature range of variation having a wider rangeof values than that of the design first target temperature range ofvariation of the target temperature of the one of the process streamsfor the first heat exchanger network design.
 16. A method as defined inclaim 1, wherein the set of process stream supply attribute valuesincludes a set of a plurality of heat capacity flow rates eachseparately associated with a different one of the plurality of processstreams and having a level of feasibility being different from the levelof feasibility for each other of the plurality of heat exchanger networkprocess variations schemes; wherein the first supply attribute valuerange of variation comprises a first heat capacity flow rate range ofvariation; wherein the second supply attribute value range of variationcomprises a second heat capacity flow rate range of variation; whereinthe method further comprises the step of applying a heat capacity flowrate range of variation of the one of the process streams of theplurality of process streams according to the second heat exchangernetwork process variations scheme defining the second heat capacity flowrate range of variation, to the heat capacity flow rate for the one ofthe process streams for the first heat exchanger network design tothereby identify a cost impact of an associated change in targettemperature thereof resulting from application of the second heatcapacity flow rate range of variation; and wherein the step ofdetermining a process-cost-impact of deviation in the first targettemperature range of variation for one or more of the process streamsfor the first heat exchanger network design is further responsive toapplication of the second heat capacity flow rate range of variation tothe heat capacity flow rate of the one of the process streams for thefirst heat exchanger network design.
 17. A method as defined in claim 1,wherein the steps of determining capital and operating costs associatedwith employing the first heat exchanger network process variationsscheme on the first heat exchanger network design and determiningcapital and operating costs associated with employing the second heatexchanger network process variations scheme on the second heat exchangernetwork design, each separately comprise performing the following steps:determining a global minimum heating energy utility, correspondingcooling energy utility, and corresponding energy cost defining a firstenergy cost value, determining a global maximum heating energy utility,corresponding cooling energy utility, and corresponding energy costdefining a second energy cost value, determining a global minimumcooling energy utility, corresponding heating energy utility, andcorresponding energy cost defining a third energy cost value,determining a global maximum cooling energy utility, correspondingheating energy utility, and corresponding energy cost defining a fourthenergy cost value, and determining a minimum energy cost value and amaximum energy cost value responsive to the determined first energy costvalue, the determined second energy cost value, the determined thirdenergy cost value, and the determined fourth energy cost value tothereby estimate an average energy operating cost; and wherein themethod further comprises the steps of determining capital and operatingcosts associated with each other of the plurality of heat exchangernetwork designs synthesized according to the corresponding each other ofthe plurality of heat exchanger network process variations schemes tothereby comparatively evaluate a cost impact of each of a correspondingplurality of different process stream flexibility levels.
 18. A methodas defined in claim 1, further comprising the step of: determining aglobal minimum cooling energy utility and a global minimum heatingenergy utility, to include analyzing an effect of a plurality ofstream-specific minimum temperature approach values (ΔTmini) on eachseparate one of a plurality of the hot process streams.
 19. A method asdefined in claim 1, further comprising the step of: determining amaximum realizable heat exchanger surface area (A) for each respectiveheat exchanger in the first heat exchanger network design according toan assigned heat exchanger network process variations scheme using amaximum realizable heat exchanger duty (Q) over a product of a heattransfer coefficient (U) and log mean temperature difference (ΔT_LMTD);wherein: Q=FCp*(Ts-Tt)=fcp*(tt-ts), ΔT_LMTD={y1*y2*(y1+y2)/2}̂0.333333,y1>=ΔT_min, y2>=ΔT_min, y1=Tt-ts, and y2=Ts-tt; and wherein: Q is theheat exchanger duty of a respective heat exchanger, FCp is the heatcapacity flow rate of a respective process stream, Ts is the supplytemperature of a respective hot process stream, Tt is the targettemperature of a respective hot process stream, ts is the supplytemperature of a respective cold process stream, tt is the targettemperature of a respective cold process stream, and ΔT_min is thestream specific minimum temperature approach for the respective processstream.
 20. A method as defined in claim 1, further comprising the stepof: determining a maximum realizable heat exchanger surface area (A) foreach heat exchanger in the first heat exchanger network design accordingto the first heat exchanger network process variations scheme using amathematical program employing a variable objective comprising eachdesign branch flow and temperature, heat exchanger input and outputtemperature, process-to-process heat exchanger duty and area, andutility heat exchanger duty and area for the first heat exchangernetwork design.
 21. A method as defined in claim 20, further comprisingthe step of: determining a total maximum realizable heat exchangersurface area for the first heat exchanger network design according tothe first heat exchanger network process variations scheme; anddetermining an optimal set of process conditions for each of theplurality of process streams that renders the total minimum realizablesurface area, the optimal set of process conditions selected from withinthe boundaries of each supply temperature, target temperature, and heatcapacity flow rate according to the first heat exchanger network processvariations scheme.
 22. A method as defined in claim 1, furthercomprising the step of: determining a minimum realizable heat exchangersurface area for each heat exchanger in the first heat exchanger networkdesign that satisfies the first heat exchanger network processvariations scheme; determining a total minimum realizable heat exchangersurface area for the first heat exchanger network design that satisfiesthe first heat exchanger network process variations scheme; anddetermining an optimal set of process conditions for each of theplurality of process streams that renders the total minimum realizablesurface area, the optimal set of process conditions selected from withinthe boundaries of each supply temperature, target temperature, and heatcapacity flow rate according to the first heat exchanger network processvariations scheme.
 23. Heat exchange network synthesizing programproduct to synthesize a grass-roots heat exchanger network for a processor cluster of processes having a plurality of hot process streams to becooled and a plurality of cold process streams to be heated and toidentify optimal heat exchanger network topology, the program productcomprising a set of instructions, stored on a tangible computer readablemedium, that when executed by a computer, cause the computer to performthe operations of: synthesizing a plurality of heat exchanger networkdesigns for a process comprising a plurality of process streams, each ofthe plurality of heat exchanger network designs synthesized according toa corresponding different one of a plurality of heat exchanger networkprocess variations schemes, each heat exchanger network exchangernetwork process variations scheme including a set of process streamsupply attribute values each separately associated with a different oneof the plurality of process streams and having a level of supplyattribute value feasibility being different from the level of supplyattribute value feasibility for each other of the plurality of heatexchanger network process variations schemes; determining capital andoperating costs associated with employing a first heat exchanger networkprocess variations scheme on a first heat exchanger network design ofthe plurality of heat exchanger network designs; determining capital andoperating costs associated with employing a second heat exchangernetwork process variations scheme on a second heat exchanger networkdesign of the plurality of heat exchanger network designs; applying asupply attribute value range of variation of one of the process streamsof the plurality of process streams according to the second heatexchanger network process variations scheme defining a second supplyattribute value range of variation to the supply attribute for the oneof the process streams for the first heat exchanger network designdefining a first supply attribute value range of variation to therebyidentify a cost impact of an associated change in target temperaturethereof resulting from application of the second supply attribute valuerange of variation thereto; and determining a process-cost-impact of adeviation in target temperature range of variation for one or more ofthe process streams for the first heat exchanger network designresponsive to application of the second supply attribute value range ofvariation to the supply attribute of the one of the process streams forthe first heat exchanger network design to thereby determine when thefirst heat exchanger network design provides a more optimal heatexchanger network design than the second heat exchanger network designand when the first heat exchanger network process variations schemecorrespondingly represents a more optimal flexibility index.
 24. Programproduct as defined in claim 23, wherein the operations further comprise:determining a target temperature range value for the one of the processstreams of the plurality of process streams defining an expectedsub-optimal target temperature range value responsive to the operationof applying the second supply attribute value range of variation to thesupply attribute of the one of the process streams for the first heatexchanger network design; determining a target temperature range valuefor each other of the-plurality of process streams responsive to theoperation of applying the second supply attribute value range ofvariation to the supply attribute of the one of the process streams forthe first heat exchanger network design; the process-cost-impactcomprising an impact of the expected sub-optimal target temperaturerange value for the one of the process streams and any changes in thetarget temperature range value for each other of the plurality ofprocess streams on total process economics resulting from application ofthe second supply attribute value range of variation on the first heatexchanger network design; and determining the first heat exchangernetwork design according to the first heat exchanger process variationsscheme to be the optimal heat exchanger network design and the firstheat exchanger network process variations scheme to represent theoptimal system-level flexibility index when the difference in capitalcost and operating cost between the first and the second heat exchangernetwork designs is higher than the process-cost-impact.
 25. Programproduct as defined in claim 23, wherein the one of the process streamsof the plurality of process streams is a first one of a plurality ofprocess streams being evaluated, wherein the supply attribute comprisessupply temperature, wherein the first supply attribute value range ofvariation comprises a first supply temperature range of variation,wherein the second supply attribute value range of variation comprises asecond supply temperature range of variation, and wherein the operationof determining a process-cost-impact further comprises the operationsof: determining an economic impact of a deviation in target temperaturerange of variation for each other of the plurality of process streamsfor the first heat exchanger network design when existing responsive toapplication of the second supply temperature range of variation of therespective process stream under evaluation according to the second heatexchanger network process variations scheme to the supply temperature ofthe respective process stream under evaluation for the first heatexchanger network design, to include performing the following operationsfor each other of the plurality of process streams: applying the secondsupply temperature range of variation of the respective process streamunder evaluation according to the second heat exchanger network processvariations scheme, to the supply temperature of the respective processstream under evaluation for the first heat exchanger network design,determining a target temperature range value for the respective processstream under evaluation defining an expected sub-optimal targettemperature range value for the respective process stream underevaluation responsive to the operation of applying the second supplytemperature range of variation of the respective process stream underevaluation according to the second heat exchanger network processvariations scheme to the supply temperature of the respective processstream under evaluation for the first heat exchanger network design tothereby determine an economic impact of the expected sub-optimal targettemperature range value for the one of the process streams on totalprocess economics, determining a target temperature range value for eachother of the plurality of process streams of the process responsive tothe operation of applying the second supply temperature range ofvariation of the respective process stream under evaluation according tothe second heat exchanger network process variations scheme to thesupply temperature of the respective process stream under evaluation forthe first heat exchanger network design to thereby determine an economicimpact of changes in the target temperature range value for each otherof the plurality of process streams on total process economics as aresult of application of the second supply temperature range ofvariation on the first exchanger network design, and determining thetotal economic cost resulting from application of the respective secondsupply temperature range of variation of the respective process streamunder evaluation according to the second heat exchanger network processvariations scheme to the supply temperature of the respective processstream under evaluation for the first heat exchanger network designresponsive to determining an economic impact of the expected sub-optimaltarget temperature range value for the respective process stream underevaluation and responsive to determining an economic impact of changesin the target temperature range value for each other of the plurality ofprocess streams; and identifying each target temperature range ofvariation of the first heat exchanger network process variations schemehaving a substantial economic impact on the process as a whole. 26.Program product as defined in claim 25, further comprising performing atleast one of the following operations: determining stream-specifictarget temperature flexibility level priority by economic impact on theprocess as a whole defining a stream-specific-flexibility-levelprioritization scheme between each of the plurality of process streamsresponsive to application of a plurality of different supply temperatureranges of variation to each of a plurality of process streams underevaluation; and assigning a stream-specific target temperatureflexibility priority level to each target temperature range of variationof each of the plurality of process streams having a substantialeconomic impact on the process as a whole.
 27. Program product asdefined in claim 23, wherein the operations further comprise:determining a stream-specific flexibility priority list for theplurality of process streams, the stream-specific flexibility prioritylist including a separate stream-specific flexibility level associatedwith each separate one of the plurality of process streams, at least twoof the stream-specific flexibility levels being different from eachother.
 28. Program product as defined in claim 23, wherein theoperations further comprise: determining a stream-specific targettemperature flexibility priority list for the plurality of processstreams, the stream-specific target temperature flexibility prioritylist including a plurality of different stream-specific targettemperature flexibility levels for each separate one of one or more ofthe plurality of process streams.
 29. Program product as defined inclaim 23, wherein the operations further comprise: determining a supplyattribute criticality list of process stream supply attribute ranges ofvariations for the plurality of process streams, the criticality listincluding a separate range of variations for each of the plurality ofprocess streams wherein a deviation in the range of variation theretoresults in a substantial economic impact on the process as a whole. 30.Program product as defined in claim 29, wherein the process streamsupply attribute ranges of variations include supply temperature rangesof variations for the supply temperatures for each of the plurality ofprocess streams, wherein the operations further comprise: determining asupply attribute criticality list of heat capacity flow rates range ofvariations for each of the plurality of process streams wherein adeviation in the heat capacity flow rate range of variation theretoresults in a substantial economic impact on the process as a whole. 31.Program product as defined in claim 23, wherein the operations furthercomprise: determining a supply attribute criticality list of processstream supply attribute ranges of variations for the plurality ofprocess streams, the criticality list including a plurality of differentranges of variations for each separate one of one or more of theplurality of process streams.
 32. Program product as defined in claim23, further comprising performing for each of the plurality of heatexchanger network designs associated with the corresponding plurality ofthe heat exchanger network process variations schemes, the operation of:analyzing a triple trade-off between estimated energy operating cost ofthe respective heat exchanger network design, estimated heat exchangernetwork capital costs, and estimated process-cost-impact at each of aplurality of individual process stream flexibility levels.
 33. Programproduct as defined in claim 23, wherein the set of process stream supplyattribute values includes a set of a plurality of supply temperatureshaving a level of supply temperature feasibility being different fromthe level of supply temperature feasibility for each other of theplurality of heat exchanger network process variations schemes; whereinthe first supply attribute value range of variation comprises a firstsupply temperature range of variation; wherein the second supplyattribute value range of variation comprises a second supply temperaturerange of variation; wherein the operation of synthesizing a plurality ofheat exchanger network designs for a process comprises the operationsof: synthesizing the first heat exchanger network design for the processaccording to the first heat exchanger network process variations scheme,the one of the process streams of the plurality of process streams forthe first heat exchanger network design including a design supplytemperature having the first supply temperature range of variationdefining a first level of flexibility according to a first probabilityand having a corresponding first design target temperature range ofvariation, and synthesizing the second heat exchanger network design forthe process according to the second heat exchanger network processvariations scheme, the one of the process streams for the second heatexchanger network design including a design supply temperature havingthe second supply temperature range of variation defining a second levelof flexibility according to a second probability and having acorresponding second target temperature range of variation, the secondsupply temperature range of variation of the one of the process streamsof the plurality process streams according to the second heat exchangernetwork variations scheme providing a higher level of flexibility thanthe first supply temperature range of variation of the one of theplurality of process streams according to the first heat exchangernetwork variations scheme and having a higher implementation cost;wherein the operation of applying a supply attribute value range ofvariation of one of the process streams of the plurality of processstreams according to the second heat exchanger network processvariations scheme to the supply attribute for the one of the processstreams for the first heat exchanger network design comprises theoperation of: assigning the second supply temperature range of variationof the one of the process streams to the supply temperature of the oneof the process streams for the first heat exchanger network design withthe supply temperature values for each other of the plurality of processstreams according to the first heat exchanger network process variationsscheme remaining unchanged, the design second supply temperature rangeof variation having a narrower range of values than that of the designfirst supply temperature range of variation of the supply temperature ofthe one of the process streams for the first heat exchanger networkdesign, the design second target temperature range of variation having awider range of values than that of the design first target temperaturerange of variation of the target temperature of the one of the processstreams for the first heat exchanger network design.
 34. Program productas defined in claim 33, wherein the second heat exchanger networkprocess variations scheme provides a higher level of flexibility thaneach other of the plurality of heat exchanger network process variationsschemes; wherein each other of the plurality of heat exchanger networkprocess variations schemes have successively lower levels of flexibilitythan that of the second heat exchanger network process variationsscheme; and wherein the operations further comprise determining aneconomic impact of a change in target temperature of one or moreassociated process streams for each other of the plurality of heatexchanger network designs defining a plurality of heat exchanger networkdesigns under evaluation resulting from application of the second supplytemperature range of variation of the supply temperature of therespective one or more process stream to the supply temperature of therespective one or more process streams of the respective heat exchangernetwork design under evaluation, to include performing the followingoperations for each of the plurality of heat exchanger network designsunder evaluation: determining capital and operating costs associatedwith the heat exchanger network design under evaluation employing thedesign specified heat exchanger network process variations scheme,applying the second supply temperature range of variation of the one ormore process streams according to the second heat exchanger networkprocess variations scheme to the supply temperature of the one or moreprocess streams for the heat exchanger network design under evaluation,determining the target temperature range value for the one or moreprocess streams defining an expected sub-optimal target temperaturerange value for the respective process stream responsive to theoperation of applying the second supply temperature range of variationof the one or more process streams according to the second heatexchanger network process variations scheme to the supply temperature ofthe one or more process streams for the heat exchanger network designunder evaluation to thereby determine an economic impact of the expectedsub-optimal target temperature range value for the one or more processstreams on total process economics, determining the target temperaturerange value for each other of the plurality of process streamsresponsive to the operation of applying the second supply temperaturerange of variation of the one or more process streams according to thesecond heat exchanger network process variations scheme to the supplytemperature of the one or more process streams for the heat exchangernetwork design under evaluation to thereby determine an economic impactof changes in the target temperature range value for each other of theplurality of process streams on total process economics, and determiningthe process-cost-impact resulting from application of the second supplytemperature range of variation of the one or more process streamsaccording to the second heat exchanger network process variations schemeto the supply temperature of the one or more process streams for theheat exchanger network design under evaluation responsive to determiningan economic impact of the expected sub-optimal target temperature rangevalue for the respective one or more process streams and responsive todetermining an economic impact of changes in the target temperaturerange value for each other of the plurality of process streams tothereby determine when the heat exchanger network design underevaluation provides a more optimal heat exchanger network design thanthe second heat exchanger network design and when the heat exchangernetwork process variations scheme associated with the respective heatexchanger network design under evaluation correspondingly represents amore optimal flexibility index.
 35. Program product as defined in claim33, wherein the second heat exchanger network process variations schemeprovides a higher level of flexibility than each other of the pluralityof heat exchanger network process variations schemes; wherein each otherof the plurality of heat exchanger network process variations schemeshave successively lower levels of flexibility than that of the secondheat exchanger network process variations scheme; wherein the operationof synthesizing a plurality of heat exchanger network designs furtherincludes identifying a third heat exchanger network process variationsscheme for a third heat exchanger network design synthesized for theprocess according to the third heat exchanger network process variationsscheme, the one of the process streams of the plurality of processstreams for the third heat exchanger network design including a designsupply temperature having a third supply temperature range of variationdefining a third level of flexibility according to a third probabilityand having a corresponding third target temperature range of variation,the third supply temperature range of variation of the one of theprocess streams according to the third heat exchanger network variationsscheme providing a lower level flexibility and higher implementationcost than both the first supply temperature range of variation of theone of the process streams according to the first heat exchanger networkvariations scheme and the second supply temperature range of variationof the one of the process streams according to the second heat exchangernetwork variations scheme; and wherein the operations further comprise:determining capital and operating costs associated with employing thethird heat exchanger network process variations scheme on the third heatexchanger network design, applying the second supply temperature rangeof variation of the one of the process streams according to the secondheat exchanger network process variations scheme to the supplytemperature for the one of the process streams for the third heatexchanger network design, with the supply temperature values for eachother of the plurality of process streams according to the third heatexchanger network process variations scheme remaining unchanged,determining the target temperature range value for the one of theprocess streams defining an expected sub-optimal target temperaturerange value for the respective process stream responsive to theoperation of applying the second supply temperature range of variationof the one of the process streams according to the second heat exchangernetwork process variations scheme to the supply temperature for the oneof the process streams for the third heat exchanger network design tothereby determine an economic impact of the expected sub-optimal targettemperature range value for the one of the process streams on totalprocess economics for the third heat exchanger network design,determining the target temperature range value for each other of theplurality of process streams responsive to the operation of applying thesecond supply temperature range of variation of the one of the processstreams according to the second heat exchanger network processvariations scheme to the supply temperature for the one of the processstreams for the third heat exchanger network design to thereby determinean economic impact of changes in the target temperature range value foreach other of the plurality of process streams on total processeconomics, determining a process-cost-impact resulting from applicationof the second supply temperature range of variation of the one of theprocess streams according to the second heat exchanger network processvariations scheme to the supply temperature of the one of the processstreams for the third heat exchanger network process variations schemeresponsive to determining an economic impact of the expected sub-optimaltarget temperature range value for the respective one or more processstreams and responsive to determining an economic impact of changes inthe target temperature range value for each other of a plurality ofprocess streams to thereby determine when the third heat exchangernetwork design provides a more optimal heat exchanger network designthan both the first and the second heat exchanger network designs andwhen the third heat exchanger network process variations schemecorresponding represents the more optimal flexibility index, anddetermining the third heat exchanger process variations scheme to be theoptimal heat exchanger network process variations scheme and torepresent the optimal flexibility index when the difference in capitalcost and operating cost between the third and the second heat exchangerdesigns is higher than the process-cost-impact resulting fromapplication of the second supply temperature range of variation of atleast a subset of the plurality of process streams according to thesecond heat exchanger network process variations scheme to therespective supply temperatures of a corresponding at least a subset ofthe plurality of process streams for the third heat exchanger networkdesign.
 36. Program product as defined in claim 33, wherein theoperation of determining capital and operating costs associated withemploying the first heat exchanger network process variations scheme onthe first heat exchanger network design includes determining a cost ofachieving the first target temperature range of variation for the one ofthe process streams with the first probability; wherein the operation ofdetermining capital and operating costs associated with employing thesecond heat exchanger network process variations scheme on the secondheat exchanger network design includes determining a cost of achievingthe second target temperature range of variation for the one of theprocess streams with the second probability; wherein the operationsfurther comprise determining a difference in capital and operating costsbetween the first and second heat exchanger network designs; wherein thefirst probability of achieving the first target temperature range ofvariation for the one of the process streams according to the first heatexchanger network variations scheme is a certain discrete value that isless than 100% when applied to the first exchanger network design;wherein the second probability of achieving the second targettemperature range of variation for the one of the process streamsaccording to the second heat exchanger network variations scheme isapproximately 100% when applied to the second heat exchanger networkdesign; and wherein the process-cost-impact includes a cost impact of adeviation of the first target temperature range value to a sub-optimallevel for a certain discrete percentage of a time responsive toapplication of the second supply temperature range of variation of thesupply temperature of the one of the process streams to the first heatexchanger network design.
 37. Program product as defined in claim 23,wherein the set of process stream supply attribute values includes a setof a plurality of heat capacity flow rates having a level of heatcapacity flow rate feasibility being different from the level of heatcapacity flow rate feasibility for each other of the plurality of heatexchanger network process variations schemes; wherein the first supplyattribute value range of variation comprises a first heat capacity flowrate range of variation; wherein the second supply attribute value rangeof variation comprises a second heat capacity flow rate range ofvariation; wherein the operation of synthesizing a plurality of heatexchanger network designs for a process comprises the operations of:synthesizing the first heat exchanger network design for the processaccording to the first heat exchanger network process variations scheme,the one of the process streams of the plurality of process streams forthe first heat exchanger network design including a design heat capacityflow rate having the first heat capacity flow rate range of variationdefining a first level of flexibility according to a first probabilityand having a corresponding first design target temperature range ofvariation, and synthesizing the second heat exchanger network design forthe process according to the second heat exchanger network processvariations scheme, the one of the process streams for the second heatexchanger network design including a design heat capacity flow ratehaving the second heat capacity flow rate range of variation defining asecond level of flexibility according to a second probability and havinga corresponding second target temperature range of variation, the secondheat capacity flow rate range of variation of the one of the processstreams of the plurality process streams according to the second heatexchanger network variations scheme providing a higher level offlexibility than the first heat capacity flow rate range of variation ofthe one of the plurality of process streams according to the first heatexchanger network variations scheme and having a higher implementationcost; wherein the operation of applying a supply attribute value rangeof variation of the one of the process streams of the plurality ofprocess streams according to the second heat exchanger network processvariations scheme to the supply attribute for the one of the processstreams for the first heat exchanger network design comprises theoperation of: assigning the second heat capacity flow rate range ofvariation of the one of the process streams to the heat capacity flowrate of the one of the process streams for the first heat exchangernetwork design with the heat capacity flow rate values for each other ofthe plurality of process streams according to the first heat exchangernetwork process variations scheme remaining unchanged, the design secondheat capacity flow rate range of variation having a narrower range ofvalues than that of the design first heat capacity flow rate range ofvariation of the heat capacity flow rate of the one of the processstreams for the first heat exchanger network design, the design secondtarget temperature range of variation having a wider range of valuesthan that of the design first target temperature range of variation ofthe target temperature of the one of the process streams for the firstheat exchanger network design.
 38. Program product as defined in claim23, wherein the set of process stream supply attribute values includes aset of a plurality of heat capacity flow rates each separatelyassociated with a different one of the plurality of process streams andhaving a level of feasibility being different from the level offeasibility for each other of the plurality of heat exchanger networkprocess variations schemes; wherein the first supply attribute valuerange of variation comprises a first heat capacity flow rate range ofvariation; wherein the second supply attribute value range of variationcomprises a second heat capacity flow rate range of variation; whereinthe operations further comprise applying a heat capacity flow rate rangeof variation of the one of the process streams of the plurality ofprocess streams according to the second heat exchanger network processvariations scheme defining the second heat capacity flow rate range ofvariation, to the heat capacity flow rate for the one of the processstreams for the first heat exchanger network design to thereby identifya cost impact of an associated change in target temperature thereofresulting from application of the second heat capacity flow rate rangeof variation; and wherein the operation of determining aprocess-cost-impact of deviation in the first target temperature rangeof variation for one or more of the process streams for the first heatexchanger network design is further responsive to application of thesecond heat capacity flow rate range of variation to the heat capacityflow rate of the one of the process streams for the first heat exchangernetwork design.
 39. Program product as defined in claim 23, wherein theoperations of determining capital and operating costs associated withemploying the first heat exchanger network process variations scheme onthe first heat exchanger network design and determining capital andoperating costs associated with employing the second heat exchangernetwork process variations scheme on the second heat exchanger networkdesign, each separately comprise performing the following operations:determining a global minimum heating energy utility, correspondingcooling energy utility, and corresponding energy cost defining a firstenergy cost value, determining a global maximum heating energy utility,corresponding cooling energy utility, and corresponding energy costdefining a second energy cost value, determining a global minimumcooling energy utility, corresponding heating energy utility, andcorresponding energy cost defining a third energy cost value,determining a global maximum cooling energy utility, correspondingheating energy utility, and corresponding energy cost defining a fourthenergy cost value, and determining a minimum energy cost value and amaximum energy cost value responsive to the determined first energy costvalue, the determined second energy cost value, the determined thirdenergy cost value, and the determined fourth energy cost value tothereby estimate an average energy operating cost; and wherein theoperations further comprise determining capital and operating costsassociated with each other of the plurality of heat exchanger networkdesigns synthesized according to the corresponding each other of theplurality of heat exchanger network process variations schemes tothereby comparatively evaluate a cost impact of each of a correspondingplurality of different process stream flexibility levels.
 40. Programproduct as defined in claim 23, wherein the operations further comprise:determining a global minimum cooling energy utility and a global minimumheating energy utility, to include analyzing an effect of a plurality ofstream-specific minimum temperature approach values (ΔTmini) on eachseparate one of a plurality of the hot process streams.
 41. Programproduct as defined in claim 23, wherein the operations further comprise:determining a maximum realizable heat exchanger surface area (A) foreach respective heat exchanger in the first heat exchanger networkdesign according to an assigned heat exchanger network processvariations scheme using a maximum realizable heat exchanger duty (Q)over a product of a heat transfer coefficient (U) and log meantemperature difference (ΔT_LMTD); wherein: Q=FCp*(Ts-Tt)=fcp*(tt-ts),ΔT_LMTD={y1*y2*(y1+y2)/2}̂0.333333, y1>=ΔT_min, y2>=ΔT_min, y1=Tt-ts, andy2=Ts-tt; and wherein: Q is the heat exchanger duty of a respective heatexchanger, FCp is the heat capacity flow rate of a respective processstream, Ts is the supply temperature of a respective hot process stream,Tt is the target temperature of a respective hot process stream, ts isthe supply temperature of a respective cold process stream, tt is thetarget temperature of a respective cold process stream, and ΔT_min isthe stream specific minimum temperature approach for the respectiveprocess stream.
 42. Program product as defined in claim 23, wherein theoperations further comprise: determining a maximum realizable heatexchanger surface area (A) for each heat exchanger in the first heatexchanger network design according to the first heat exchanger networkprocess variations scheme using a mathematical program employing avariable objective comprising each design branch flow and temperature,heat exchanger input and output temperature, process-to-process heatexchanger duty and area, and utility heat exchanger duty and area forthe first heat exchanger network design.
 43. Program product as definedin claim 42, wherein the operations further comprise: determining atotal maximum realizable heat exchanger surface area for the first heatexchanger network design according to the first heat exchanger networkprocess variations scheme; and determining an optimal set of processconditions for each of the plurality of process streams that renders thetotal minimum realizable surface area, the optimal set of processconditions selected from within the boundaries of each supplytemperature, target temperature, and heat capacity flow rate accordingto the first heat exchanger network process variations scheme. 44.Program product as defined in claim 23, wherein the operations furthercomprise: determining a minimum realizable heat exchanger surface areafor each heat exchanger in the first heat exchanger network design thatsatisfies the first heat exchanger network process variations scheme;determining a total minimum realizable heat exchanger surface area forthe first heat exchanger network design that satisfies the first heatexchanger network process variations scheme; and determining an optimalset of process conditions for each of the plurality of process streamsthat renders the total minimum realizable surface area, the optimal setof process conditions selected from within the boundaries of each supplytemperature, target temperature, and heat capacity flow rate accordingto the first heat exchanger network process variations scheme.
 45. Asystem to synthesize a grass-roots heat exchanger network for a processor cluster of processes having a plurality of hot process streams to becooled and a plurality of cold process streams to be heated and toidentify optimal heat exchanger network topology, the system comprising:a heat exchange network synthesizing computer having a processor andmemory in communication with the processor to store software anddatabase records therein; at least one database stored in memoryaccessible to the heat exchange network synthesizing computer,comprising data representing a plurality of heat exchanger networkprocess variations schemes, each heat exchanger network exchangernetwork process variations scheme including a set of process streamsupply attribute values each separately associated with a different oneof the plurality of process streams and having a level of supplyattribute value feasibility being different from the level of supplyattribute value feasibility for each other of the plurality of heatexchanger network process variations schemes, the set of process streamsupply attribute values including one or more of the following: a set ofa plurality of supply temperatures having a level of supply temperaturefeasibility being different from the level of supply temperaturefeasibility for each other of the plurality of heat exchanger networkprocess variations schemes, and a set of a plurality of heat capacityflow rates having a level of heat capacity flow rate feasibility beingdifferent from the level of heat capacity flow rate feasibility for eachother of the plurality of heat exchanger network process variationsschemes; and heat exchange network synthesizing program product storedin the memory of the heat exchange network synthesizing computer tosynthesize a grass-roots heat exchanger network for the plurality of hotprocess streams to be cooled and the plurality of cold process streamsto be heated, the program product including instructions that whenexecuted by the heat exchange network synthesizing computer cause thecomputer to perform the operations of: synthesizing a plurality of heatexchanger network designs for a process comprising a plurality ofprocess streams, each of the plurality of heat exchanger network designssynthesized according to a corresponding different one of the pluralityof heat exchanger network process variations schemes, determiningcapital and operating costs associated with employing a first heatexchanger network process variations scheme on a first heat exchangernetwork design of the plurality of heat exchanger network designs,determining capital and operating costs associated with employing asecond heat exchanger network process variations scheme on a second heatexchanger network design of the plurality of heat exchanger networkdesigns, applying a supply attribute value range of variation of one ofthe process streams of the plurality of process streams according to thesecond heat exchanger network process variations scheme defining asecond supply attribute value range of variation to the supply attributefor the one of the process streams for the first heat exchanger networkdesign defining a first supply attribute value range of variation tothereby identify a cost impact of an associated change in targettemperature thereof resulting from application of the second supplyattribute value range of variation thereto, the first supply attributevalue range of variation comprising one or more of the following: afirst supply temperature range of variation and a first heat capacityflow rate range of variation, the second supply attribute value range ofvariation comprising one or more of the following: a second supplytemperature range of variation and a second heat capacity flow raterange of variation, and determining a process-cost-impact of a deviationin target temperature range of variation for one or more of the processstreams for the first heat exchanger network design responsive toapplication of the second supply attribute value range of variation tothe supply attribute of the one of the process streams for the firstheat exchanger network design, analyzing a triple trade-off betweenestimated energy operating cost of the respective heat exchanger networkdesign, estimated heat exchanger network capital costs, and estimatedprocess-cost-impact to thereby determine when the first heat exchangernetwork design provides a more optimal heat exchanger network designthan the second heat exchanger network design and when the first heatexchanger network process variations scheme correspondingly represents amore optimal flexibility index.
 46. A system as defined in claim 45,wherein the operations further comprise: determining a targettemperature range value for the one of the process streams of theplurality of process streams defining an expected sub-optimal targettemperature range value responsive to the operation of applying thesecond supply attribute value range of variation to the supply attributeof the one of the process streams for the first heat exchanger networkdesign; determining a target temperature range value for each other ofthe plurality of process streams responsive to the operation of applyingthe second supply attribute value range of variation to the supplyattribute of the one of the process streams for the first heat exchangernetwork design; the process-cost-impact comprising an impact of theexpected sub-optimal target temperature range value for the one of theprocess streams and any changes in the target temperature range valuefor each other of the plurality of process streams on total processeconomics resulting from application of the second supply attributevalue range of variation on the first heat exchanger network design; anddetermining the first heat exchanger network design according to thefirst heat exchanger process variations scheme to be the optimal heatexchanger network design and the first heat exchanger network processvariations scheme to represent the optimal system-level flexibilityindex when the difference in capital cost and operating cost between thefirst and the second heat exchanger network designs is higher than theprocess-cost-impact.
 47. A system as defined in claim 45, wherein theone of the process streams of the plurality of process streams is afirst one of a plurality of process streams being evaluated, wherein thesupply attribute comprises supply temperature, wherein the first supplyattribute value range of variation comprises a first supply temperaturerange of variation, wherein the second supply attribute value range ofvariation comprises a second supply temperature range of variation, andwherein the operation of determining a process-cost-impact furthercomprises the operations of: determining an economic impact of adeviation in target temperature range of variation for each other of theplurality of process streams for the first heat exchanger network designwhen existing responsive to application of the second supply temperaturerange of variation of the respective process stream under evaluationaccording to the second heat exchanger network process variations schemeto the supply temperature of the respective process stream underevaluation for the first heat exchanger network design, to includeperforming the following operations for each other of the plurality ofprocess streams: applying the second supply temperature range ofvariation of the respective process stream under evaluation according tothe second heat exchanger network process variations scheme, to thesupply temperature of the respective process stream under evaluation forthe first heat exchanger network design, determining a targettemperature range value for the respective process stream underevaluation defining an expected sub-optimal target temperature rangevalue for the respective process stream under evaluation responsive tothe operation of applying the second supply temperature range ofvariation of the respective process stream under evaluation according tothe second heat exchanger network process variations scheme to thesupply temperature of the respective process stream under evaluation forthe first heat exchanger network design to thereby determine an economicimpact of the expected sub-optimal target temperature range value forthe one of the process streams on total process economics, determining atarget temperature range value for each other of the plurality ofprocess streams of the process responsive to the operation of applyingthe second supply temperature range of variation of the respectiveprocess stream under evaluation according to the second heat exchangernetwork process variations scheme to the supply temperature of therespective process stream under evaluation for the first heat exchangernetwork design to thereby determine an economic impact of changes in thetarget temperature range value for each other of the plurality ofprocess streams on total process economics as a result of application ofthe second supply temperature range of variation on the first exchangernetwork design, and determining the total economic cost resulting fromapplication of the respective second supply temperature range ofvariation of the respective process stream under evaluation according tothe second heat exchanger network process variations scheme to thesupply temperature of the respective process stream under evaluation forthe first heat exchanger network design responsive to determining aneconomic impact of the expected sub-optimal target temperature rangevalue for the respective process stream under evaluation and responsiveto determining an economic impact of changes in the target temperaturerange value for each other of the plurality of process streams; andidentifying each target temperature range of variation of the first heatexchanger network process variations scheme having a substantialeconomic impact on the process as a whole.
 48. A system as defined inclaim 47, wherein the operations further comprise: analyzing, for eachof the plurality of heat exchanger network designs associated with thecorresponding plurality of the heat exchanger network process variationsschemes, a triple trade-off between estimated energy operating cost ofthe respective heat exchanger network design, estimated heat exchangernetwork capital costs, and estimated process-cost-impact at each of aplurality of individual process stream flexibility levels; andperforming at least one of the following operations: determiningstream-specific target temperature flexibility level priority byeconomic impact on the process as a whole defining astream-specific-flexibility-level prioritization scheme between each ofthe plurality of process streams responsive to application of aplurality of different supply temperature ranges of variation to each ofa plurality of process streams under evaluation, and assigning astream-specific target temperature flexibility priority level to eachtarget temperature range of variation of each of the plurality ofprocess streams having a substantial economic impact on the process as awhole.
 49. A system as defined in claim 45, wherein the operationsfurther comprise performing one or more of the following: determining astream-specific flexibility priority list for the plurality of processstreams, the stream-specific flexibility priority list including aseparate stream-specific flexibility level associated with each separateone of the plurality of process streams, at least two of thestream-specific flexibility levels being different from each other; anddetermining a stream-specific target temperature flexibility prioritylist for the plurality of process streams, the stream-specific targettemperature flexibility priority list including a plurality of differentstream-specific target temperature flexibility levels for each separateone of one or more of the plurality of process streams.
 50. A system asdefined in claim 45, wherein the operations further comprise performingone or more of the following: determining a supply attribute criticalitylist of process stream supply temperature ranges of variations for theplurality of process streams, the criticality list including a separaterange of variations for each of the plurality of process streams whereina deviation in the range of variation thereto results in a substantialeconomic impact on the process as a whole; and determining a supplyattribute criticality list of heat capacity flow rates range ofvariations for each of the plurality of process streams wherein adeviation in the heat capacity flow rate range of variation theretoresults in a substantial economic impact on the process as a whole. 51.A system as defined in claim 45, wherein the first supply attributevalue range of variation comprises the first supply temperature range ofvariation; wherein the second supply attribute value range of variationcomprises the second supply temperature range of variation; wherein theoperation of synthesizing a plurality of heat exchanger network designsfor a process comprises the operations of: synthesizing the first heatexchanger network design for the process according to the first heatexchanger network process variations scheme, the one of the processstreams of the plurality of process streams for the first heat exchangernetwork design including a design supply temperature having the firstsupply temperature range of variation defining a first level offlexibility according to a first probability and having a correspondingfirst design target temperature range of variation, and synthesizing thesecond heat exchanger network design for the process according to thesecond heat exchanger network process variations scheme, the one of theprocess streams for the second heat exchanger network design including adesign supply temperature having the second supply temperature range ofvariation defining a second level of flexibility according to a secondprobability and having a corresponding second target temperature rangeof variation, the second supply temperature range of variation of theone of the process streams of the plurality process streams according tothe second heat exchanger network variations scheme providing a higherlevel of flexibility than the first supply temperature range ofvariation of the one of the plurality of process streams according tothe first heat exchanger network variations scheme and having a higherimplementation cost; wherein the operation of applying a supplyattribute value range of variation of one of the process streams of theplurality of process streams according to the second heat exchangernetwork process variations scheme to the supply attribute for the one ofthe process streams for the first heat exchanger network designcomprises the operation of: assigning the second supply temperaturerange of variation of the one of the process streams to the supplytemperature of the one of the process streams for the first heatexchanger network design with the supply temperature values for eachother of the plurality of process streams according to the first heatexchanger network process variations scheme remaining unchanged, thedesign second supply temperature range of variation having a narrowerrange of values than that of the design first supply temperature rangeof variation of the supply temperature of the one of the process streamsfor the first heat exchanger network design, the design second targettemperature range of variation having a wider range of values than thatof the design first target temperature range of variation of the targettemperature of the one of the process streams for the first heatexchanger network design.
 52. A system as defined in claim 45, whereinthe second heat exchanger network process variations scheme provides ahigher level of flexibility than each other of the plurality of heatexchanger network process variations schemes; wherein each other of theplurality of heat exchanger network process variations schemes havesuccessively lower levels of flexibility than that of the second heatexchanger network process variations scheme; and wherein the operationsfurther comprise determining an economic impact of a change in targettemperature of one or more associated process streams for each other ofthe plurality of heat exchanger network designs defining a plurality ofheat exchanger network designs under evaluation resulting fromapplication of the second supply temperature range of variation of thesupply temperature of the respective one or more process stream to thesupply temperature of the respective one or more process streams of therespective heat exchanger network design under evaluation, to includeperforming the following operations for each of the plurality of heatexchanger network designs under evaluation: determining capital andoperating costs associated with the heat exchanger network design underevaluation employing the design specified heat exchanger network processvariations scheme, applying the second supply temperature range ofvariation of the one or more process streams according to the secondheat exchanger network process variations scheme to the supplytemperature of the one or more process streams for the heat exchangernetwork design under evaluation, determining the target temperaturerange value for the one or more process streams defining an expectedsub-optimal target temperature range value for the respective processstream responsive to the operation of applying the second supplytemperature range of variation of the one or more process streamsaccording to the second heat exchanger network process variations schemeto the supply temperature of the one or more process streams for theheat exchanger network design under evaluation to thereby determine aneconomic impact of the expected sub-optimal target temperature rangevalue for the one or more process streams on total process economics,determining the target temperature range value for each other of theplurality of process streams responsive to the operation of applying thesecond supply temperature range of variation of the one or more processstreams according to the second heat exchanger network processvariations scheme to the supply temperature of the one or more processstreams for the heat exchanger network design under evaluation tothereby determine an economic impact of changes in the targettemperature range value for each other of the plurality of processstreams on total process economics, and determining theprocess-cost-impact resulting from application of the second supplytemperature range of variation of the one or more process streamsaccording to the second heat exchanger network process variations schemeto the supply temperature of the one or more process streams for theheat exchanger network design under evaluation responsive to determiningan economic impact of the expected sub-optimal target temperature rangevalue for the respective one or more process streams and responsive todetermining an economic impact of changes in the target temperaturerange value for each other of the plurality of process streams tothereby determine when the heat exchanger network design underevaluation provides a more optimal heat exchanger network design thanthe second heat exchanger network design and when the heat exchangernetwork process variations scheme associated with the respective heatexchanger network design under evaluation correspondingly represents amore optimal flexibility index.
 53. A system as defined in claim 45,wherein the second heat exchanger network process variations schemeprovides a higher level of flexibility than each other of the pluralityof heat exchanger network process variations schemes; wherein each otherof the plurality of heat exchanger network process variations schemeshave successively lower levels of flexibility than that of the secondheat exchanger network process variations scheme; wherein the operationof synthesizing a plurality of heat exchanger network designs furtherincludes identifying a third heat exchanger network process variationsscheme for a third heat exchanger network design synthesized for theprocess according to the third heat exchanger network process variationsscheme, the one of the process streams of the plurality of processstreams for the third heat exchanger network design including a designsupply temperature having a third supply temperature range of variationdefining a third level of flexibility according to a third probabilityand having a corresponding third target temperature range of variation,the third supply temperature range of variation of the one of theprocess streams according to the third heat exchanger network variationsscheme providing a lower level flexibility and higher implementationcost than both the first supply temperature range of variation of theone of the process streams according to the first heat exchanger networkvariations scheme and the second supply temperature range of variationof the one of the process streams according to the second heat exchangernetwork variations scheme; and wherein the operations further comprise:determining capital and operating costs associated with employing thethird heat exchanger network process variations scheme on the third heatexchanger network design, applying the second supply temperature rangeof variation of the one of the process streams according to the secondheat exchanger network process variations scheme to the supplytemperature for the one of the process streams for the third heatexchanger network design, with the supply temperature values for eachother of the plurality of process streams according to the third heatexchanger network process variations scheme remaining unchanged,determining the target temperature range value for the one of theprocess streams defining an expected sub-optimal target temperaturerange value for the respective process stream responsive to theoperation of applying the second supply temperature range of variationof the one of the process streams according to the second heat exchangernetwork process variations scheme to the supply temperature for the oneof the process streams for the third heat exchanger network design tothereby determine an economic impact of the expected sub-optimal targettemperature range value for the one of the process streams on totalprocess economics for the third heat exchanger network design,determining the target temperature range value for each other of theplurality of process streams responsive to the operation of applying thesecond supply temperature range of variation of the one of the processstreams according to the second heat exchanger network processvariations scheme to the supply temperature for the one of the processstreams for the third heat exchanger network design to thereby determinean economic impact of changes in the target temperature range value foreach other of the plurality of process streams on total processeconomics, determining a process-cost-impact resulting from applicationof the second supply temperature range of variation of the one of theprocess streams according to the second heat exchanger network processvariations scheme to the supply temperature of the one of the processstreams for the third heat exchanger network process variations schemeresponsive to determining an economic impact of the expected sub-optimaltarget temperature range value for the respective one or more processstreams and responsive to determining an economic impact of changes inthe target temperature range value for each other of the plurality ofprocess streams to thereby determine when the third heat exchangernetwork design provides a more optimal heat exchanger network designthan both the first and the second heat exchanger network designs andwhen the third heat exchanger network process variations schemecorresponding represents the more optimal flexibility index, anddetermining the third heat exchanger process variations scheme to be theoptimal heat exchanger network process variations scheme and torepresent the optimal flexibility index when the difference in capitalcost and operating cost between the third and the second heat exchangerdesigns is higher than the process-cost-impact resulting fromapplication of the second supply temperature range of variation of atleast a subset of the plurality of process streams according to thesecond heat exchanger network process variations scheme to therespective supply temperatures of a corresponding at least a subset ofthe plurality of process streams for the third heat exchanger networkdesign.
 54. A system as defined in claim 45, wherein the operation ofdetermining capital and operating costs associated with employing thefirst heat exchanger network process variations scheme on the first heatexchanger network design includes determining a cost of achieving thefirst target temperature range of variation for the one of the processstreams with the first probability; wherein the operation of determiningcapital and operating costs associated with employing the second heatexchanger network process variations scheme on the second heat exchangernetwork design includes determining a cost of achieving the secondtarget temperature range of variation for the one of the process streamswith the second probability; wherein the operations further comprisedetermining a difference in capital and operating costs between thefirst and second heat exchanger network designs; wherein the firstprobability of achieving the first target temperature range of variationfor the one of the process streams according to the first heat exchangernetwork variations scheme is a certain discrete value that is less than100% when applied to the first exchanger network design; wherein thesecond probability of achieving the second target temperature range ofvariation for the one of the process streams according to the secondheat exchanger network variations scheme is approximately 100% whenapplied to the second heat exchanger network design; and wherein theprocess-cost-impact includes a cost impact of a deviation of the firsttarget temperature range value to a sub-optimal level for a certaindiscrete percentage of a time responsive to application of the secondsupply temperature range of variation of the supply temperature of theone of the process streams to the first heat exchanger network design.55. A system as defined in claim 45, wherein the first supply attributevalue range of variation comprises the first heat capacity flow raterange of variation; wherein the second supply attribute value range ofvariation comprises the second heat capacity flow rate range ofvariation; wherein the operation of synthesizing a plurality of heatexchanger network designs for a process comprises the operations of:synthesizing the first heat exchanger network design for the processaccording to the first heat exchanger network process variations scheme,the one of the process streams of the plurality of process streams forthe first heat exchanger network design including a design heat capacityflow rate having the first heat capacity flow rate range of variationdefining a first level of flexibility according to a first probabilityand having a corresponding first design target temperature range ofvariation, and synthesizing the second heat exchanger network design forthe process according to the second heat exchanger network processvariations scheme, the one of the process streams for the second heatexchanger network design including a design heat capacity flow ratehaving the second heat capacity flow rate range of variation defining asecond level of flexibility according to a second probability and havinga corresponding second target temperature range of variation, the secondheat capacity flow rate range of variation of the one of the processstreams of the plurality process streams according to the second heatexchanger network variations scheme providing a higher level offlexibility than the first heat capacity flow rate range of variation ofthe one of the plurality of process streams according to the first heatexchanger network variations scheme and having a higher implementationcost; wherein the operation of applying a supply attribute value rangeof variation of the one of the process streams of the plurality ofprocess streams according to the second heat exchanger network processvariations scheme to the supply attribute for the one of the processstreams for the first heat exchanger network design comprises theoperation of: assigning the second heat capacity flow rate range ofvariation of the one of the process streams to the heat capacity flowrate of the one of the process streams for the first heat exchangernetwork design with the heat capacity flow rate values for each other ofthe plurality of process streams according to the first heat exchangernetwork process variations scheme remaining unchanged, the design secondheat capacity flow rate range of variation having a narrower range ofvalues than that of the design first heat capacity flow rate range ofvariation of the heat capacity flow rate of the one of the processstreams for the first heat exchanger network design, the design secondtarget temperature range of variation having a wider range of valuesthan that of the design first target temperature range of variation ofthe target temperature of the one of the process streams for the firstheat exchanger network design.
 56. A system as defined in claim 45, flowrate wherein the first supply attribute value range of variationcomprises the first heat capacity flow rate range of variation; whereinthe second supply attribute value range of variation comprises thesecond heat capacity flow rate range of variation; wherein theoperations further comprise applying a heat capacity flow rate range ofvariation of the one of the process streams of the plurality of processstreams according to the second heat exchanger network processvariations scheme defining the second heat capacity flow rate range ofvariation, to the heat capacity flow rate for the one of the processstreams for the first heat exchanger network design to thereby identifya cost impact of an associated change in target temperature thereofresulting from application of the second heat capacity flow rate rangeof variation; and wherein the operation of determining aprocess-cost-impact of deviation in the first target temperature rangeof variation for one or more of the process streams for the first heatexchanger network design is further responsive to application of thesecond heat capacity flow rate range of variation to the heat capacityflow rate of the one of the process streams for the first heat exchangernetwork design.